[Android NDK ] Passing JNI Arrays

<div class="wp_syntax" style="background-color: #f9f9f9; border: 1px solid silver; color: #110000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; margin: 0px 0px 1.5em; overflow-x: auto; overflow-y: hidden; padding: 0px; width: 3305.609375px;"><br /><table style="border-collapse: collapse !important; border: none !important; margin: 0px !important; padding: 0px !important; width: 3305px;"><tbody style="margin: 0px; padding: 0px;"><tr style="margin: 0px; padding: 0px;"><td class="line_numbers" style="border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important;"><pre style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: rgb(221, 238, 255) !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; color: gray !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; text-align: right !important; width: 16px !important;">1<br />2<br />3<br />4<br />5<br />6<br />7<br />8<br />9<br /></pre></td><td class="code" style="background-color: #eeeeee; background-image: linear-gradient(transparent 50%, rgba(255, 255, 255, 0.901961) 50%); background-size: 1px 32px; border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important; width: 3281px;"><pre class="c" style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: transparent !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; width: auto !important;">JNIExport jint JNICALL Java_IntArray_sumArray<span style="color: #009900; margin: 0px; padding: 0px;">(</span>JNIEnv <span style="color: #339933; margin: 0px; padding: 0px;">*</span>env<span style="color: #339933; margin: 0px; padding: 0px;">,</span> jobject obj<span style="color: #339933; margin: 0px; padding: 0px;">,</span><br /> jintArray arr<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> jsize len <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #339933; margin: 0px; padding: 0px;">*</span>env<span style="color: #339933; margin: 0px; padding: 0px;">-></span>GetArrayLength<span style="color: #009900; margin: 0px; padding: 0px;">(</span>env<span style="color: #339933; margin: 0px; padding: 0px;">,</span>arr<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> jint <span style="color: #339933; margin: 0px; padding: 0px;">*</span>body <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #339933; margin: 0px; padding: 0px;">*</span>env<span style="color: #339933; margin: 0px; padding: 0px;">-></span>GetIntArrayElements<span style="color: #009900; margin: 0px; padding: 0px;">(</span>env<span style="color: #339933; margin: 0px; padding: 0px;">,</span>arr<span style="color: #339933; margin: 0px; padding: 0px;">,</span><span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="color: #b1b100; margin: 0px; padding: 0px;">for</span> <span style="color: #009900; margin: 0px; padding: 0px;">(</span>jint i <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> i <span style="color: #339933; margin: 0px; padding: 0px;"><</span> len<span style="color: #339933; margin: 0px; padding: 0px;">;</span> <span style="color: #339933; margin: 0px; padding: 0px;">++</span>i<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> sum <span style="color: #339933; margin: 0px; padding: 0px;">+=</span> body<span style="color: #009900; margin: 0px; padding: 0px;">[</span>i<span style="color: #009900; margin: 0px; padding: 0px;">]</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">}</span><br /> <span style="color: #339933; margin: 0px; padding: 0px;">*</span>env<span style="color: #339933; margin: 0px; padding: 0px;">-></span>ReleastIntArrayElements<span style="color: #009900; margin: 0px; padding: 0px;">(</span>env<span style="color: #339933; margin: 0px; padding: 0px;">,</span> arr<span style="color: #339933; margin: 0px; padding: 0px;">,</span> body<span style="color: #339933; margin: 0px; padding: 0px;">,</span> <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /><span style="color: #009900; margin: 0px; padding: 0px;">}</span></pre></td></tr></tbody></table></div><table border="0" cellpadding="0" cellspacing="0" class="tbl" style="background-color: #eeeeee; border-collapse: collapse; border: 1px solid rgb(17, 17, 17); color: black; font-family: Arial, Helvetica, sans-serif; font-size: 13px; height: 10px; margin: 0px; padding: 0px 0px 0px 20px; width: 100%px;"><tbody style="margin: 0px; padding: 0px;"><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;" width="30%"><strong style="margin: 0px; padding: 0px;">JNI Function</strong></td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;" width="70%"><strong style="margin: 0px; padding: 0px;">Description</strong></td></tr><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Get<Type>ArrayRegion<br />Set<Type>ArrayRegion</td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Copies the contents of primitive arrays to or from a pre-allocated C buffer.</td></tr><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Get<Type>ArrayElements<br />Release<Type>ArrayElements</td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Obtains a pointer to the contents of a primitive array. May return a copy of the array.</td></tr><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">GetArrayLength</td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Returns the number of elements in the array.</td></tr><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">New<Type>Array</td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Creates an array with the given length.</td></tr><tr style="margin: 0px; padding: 0px;"><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">GetPrimitiveArrayCritical<br />ReleasePrimitiveArrayCritical</td><td style="border: 1px solid rgb(204, 204, 204); font-size: 10pt; margin: 0px; padding: 6px;">Obtains or releases a pointer to the contents of a primitive array. These functions allow virtual machines to disable garbage collection while the native code accesses the contents of primitive arrays.</td></tr></tbody></table><div style="background-color: #3b5998; font-family: Tahoma, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 14pt; padding: 5px 0px; text-align: justify;"><strong style="margin: 0px; padding: 0px;">JNI Array Example program</strong></div><div class="wp_syntax" style="background-color: #f9f9f9; border: 1px solid silver; color: #110000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; margin: 0px 0px 1.5em; overflow-x: auto; overflow-y: hidden; padding: 0px; width: 3305.609375px;"><table style="border-collapse: collapse !important; border: none !important; margin: 0px !important; padding: 0px !important; width: 3305px;"><tbody style="margin: 0px; padding: 0px;"><tr style="margin: 0px; padding: 0px;"><td class="line_numbers" style="border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important;"><pre style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: rgb(221, 238, 255) !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; color: gray !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; text-align: right !important; width: 16px !important;">1<br />2<br />3<br />4<br />5<br />6<br />7<br />8<br />9<br />10<br />11<br />12<br />13<br />14<br />15<br />16<br />17<br />18<br />19<br />20<br />21<br />22<br />23<br />24<br />25<br />26<br />27<br />28<br /></pre></td><td class="code" style="background-color: #eeeeee; background-image: linear-gradient(transparent 50%, rgba(255, 255, 255, 0.901961) 50%); background-size: 1px 32px; border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important; width: 3281px;"><pre class="java" style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: transparent !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; width: auto !important;"><span style="font-weight: bold; margin: 0px; padding: 0px;">class</span> SortArray <span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> <span style="font-weight: bold; margin: 0px; padding: 0px;">private</span> <span style="font-weight: bold; margin: 0px; padding: 0px;">native</span> <span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span><span style="color: #009900; margin: 0px; padding: 0px;">[</span><span style="color: #009900; margin: 0px; padding: 0px;">]</span> sort<span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span><span style="color: #009900; margin: 0px; padding: 0px;">[</span><span style="color: #009900; margin: 0px; padding: 0px;">]</span> arr<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> <span style="color: #666666; font-style: italic; margin: 0px; padding: 0px;">//native method </span><br /> <br /> <span style="font-weight: bold; margin: 0px; padding: 0px;">static</span> <span style="color: #666666; font-style: italic; margin: 0px; padding: 0px;">//static initializer code</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> <span style="color: #003399; margin: 0px; padding: 0px;">System</span>.<span style="color: #006633; margin: 0px; padding: 0px;">loadLibrary</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: blue; margin: 0px; padding: 0px;">"SortArray"</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">}</span> <br /> <br /> <span style="font-weight: bold; margin: 0px; padding: 0px;">public</span> <span style="font-weight: bold; margin: 0px; padding: 0px;">static</span> <span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">void</span> main<span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: #003399; margin: 0px; padding: 0px;">String</span><span style="color: #009900; margin: 0px; padding: 0px;">[</span><span style="color: #009900; margin: 0px; padding: 0px;">]</span> args<span style="color: #009900; margin: 0px; padding: 0px;">)</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> <span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span> iArr<span style="color: #009900; margin: 0px; padding: 0px;">[</span><span style="color: #009900; margin: 0px; padding: 0px;">]</span> <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #009900; margin: 0px; padding: 0px;">{</span><span style="color: #cc66cc; margin: 0px; padding: 0px;">4</span>,<span style="color: #cc66cc; margin: 0px; padding: 0px;">5</span>,<span style="color: #cc66cc; margin: 0px; padding: 0px;">2</span>,<span style="color: #cc66cc; margin: 0px; padding: 0px;">7</span>,<span style="color: #cc66cc; margin: 0px; padding: 0px;">1</span>,<span style="color: #cc66cc; margin: 0px; padding: 0px;">9</span><span style="color: #009900; margin: 0px; padding: 0px;">}</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> <span style="color: #666666; font-style: italic; margin: 0px; padding: 0px;">// Input array</span><br /> <span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span> oArr<span style="color: #009900; margin: 0px; padding: 0px;">[</span><span style="color: #009900; margin: 0px; padding: 0px;">]</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> <span style="color: #666666; font-style: italic; margin: 0px; padding: 0px;">//Output array</span><br /> <br /> SortArray arr <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="font-weight: bold; margin: 0px; padding: 0px;">new</span> SortArray<span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <br /> <span style="color: #003399; margin: 0px; padding: 0px;">System</span>.<span style="color: #006633; margin: 0px; padding: 0px;">out</span>.<span style="color: #006633; margin: 0px; padding: 0px;">println</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: blue; margin: 0px; padding: 0px;">"Unsorted array: "</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="font-weight: bold; margin: 0px; padding: 0px;">for</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span> i <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #cc66cc; margin: 0px; padding: 0px;">0</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> i <span style="color: #339933; margin: 0px; padding: 0px;"><</span> iArr.<span style="color: #006633; margin: 0px; padding: 0px;">length</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> i<span style="color: #339933; margin: 0px; padding: 0px;">++</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> <span style="color: #003399; margin: 0px; padding: 0px;">System</span>.<span style="color: #006633; margin: 0px; padding: 0px;">out</span>.<span style="color: #006633; margin: 0px; padding: 0px;">println</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span>iArr<span style="color: #009900; margin: 0px; padding: 0px;">[</span>i<span style="color: #009900; margin: 0px; padding: 0px;">]</span> <span style="color: #339933; margin: 0px; padding: 0px;">+</span> <span style="color: blue; margin: 0px; padding: 0px;">" "</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">}</span><br /> <br /> oArr <span style="color: #339933; margin: 0px; padding: 0px;">=</span> arr.<span style="color: #006633; margin: 0px; padding: 0px;">sort</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span>iArr<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <br /> <span style="color: #003399; margin: 0px; padding: 0px;">System</span>.<span style="color: #006633; margin: 0px; padding: 0px;">out</span>.<span style="color: #006633; margin: 0px; padding: 0px;">println</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: blue; margin: 0px; padding: 0px;">"Sorted array: "</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="font-weight: bold; margin: 0px; padding: 0px;">for</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span><span style="color: #000066; font-weight: bold; margin: 0px; padding: 0px;">int</span> i <span style="color: #339933; margin: 0px; padding: 0px;">=</span> <span style="color: #cc66cc; margin: 0px; padding: 0px;">0</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> i <span style="color: #339933; margin: 0px; padding: 0px;"><</span> oArr.<span style="color: #006633; margin: 0px; padding: 0px;">length</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span> i<span style="color: #339933; margin: 0px; padding: 0px;">++</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /> <span style="color: #003399; margin: 0px; padding: 0px;">System</span>.<span style="color: #006633; margin: 0px; padding: 0px;">out</span>.<span style="color: #006633; margin: 0px; padding: 0px;">println</span><span style="color: #009900; margin: 0px; padding: 0px;">(</span>oArr<span style="color: #009900; margin: 0px; padding: 0px;">[</span>i<span style="color: #009900; margin: 0px; padding: 0px;">]</span> <span style="color: #339933; margin: 0px; padding: 0px;">+</span> <span style="color: blue; margin: 0px; padding: 0px;">" "</span><span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">}</span><br /> <span style="color: #009900; margin: 0px; padding: 0px;">}</span><br /><span style="color: #009900; margin: 0px; padding: 0px;">}</span></pre></td></tr></tbody></table></div><div class="wp_syntax" style="background-color: #f9f9f9; border: 1px solid silver; color: #110000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; margin: 0px 0px 1.5em; overflow-x: auto; overflow-y: hidden; padding: 0px; width: 3305.609375px;"><table style="border-collapse: collapse !important; border: none !important; margin: 0px !important; padding: 0px !important; width: 3305px;"><tbody style="margin: 0px; padding: 0px;"><tr style="margin: 0px; padding: 0px;"><td class="line_numbers" style="border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important;"><pre style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: rgb(221, 238, 255) !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; color: gray !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; text-align: right !important; width: 16px !important;">1<br />2<br />3<br />4<br />5<br />6<br />7<br />8<br />9<br />10<br />11<br />12<br />13<br />14<br />15<br />16<br />17<br />18<br />19<br />20<br />21<br /></pre></td><td class="code" style="background-color: #eeeeee; background-image: linear-gradient(transparent 50%, rgba(255, 255, 255, 0.901961) 50%); background-size: 1px 32px; border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important; width: 3281px;"><pre class="c" style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: transparent !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; width: auto !important;"><span style="color: grey; font-style: italic; margin: 0px; padding: 0px;">/* DO NOT EDIT THIS FILE - it is machine generated */</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#include</span><br /><span style="color: grey; font-style: italic; margin: 0px; padding: 0px;">/* Header for class SortArray */</span><br /> <br /><span style="color: #339933; margin: 0px; padding: 0px;">#ifndef _Included_SortArray</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#define _Included_SortArray</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#ifdef __cplusplus</span><br /><span style="font-weight: bold; margin: 0px; padding: 0px;">extern</span> <span style="color: red; margin: 0px; padding: 0px;">"C"</span> <span style="color: #009900; margin: 0px; padding: 0px;">{</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#endif</span><br /><span style="color: grey; font-style: italic; margin: 0px; padding: 0px;">/*<br /> * Class: SortArray<br /> * Method: sort<br /> * Signature: ([I)[I<br /> */</span><br />JNIEXPORT jintArray JNICALL Java_SortArray_sort<br /> <span style="color: #009900; margin: 0px; padding: 0px;">(</span>JNIEnv <span style="color: #339933; margin: 0px; padding: 0px;">*,</span> jobject<span style="color: #339933; margin: 0px; padding: 0px;">,</span> jintArray<span style="color: #009900; margin: 0px; padding: 0px;">)</span><span style="color: #339933; margin: 0px; padding: 0px;">;</span><br /> <br /><span style="color: #339933; margin: 0px; padding: 0px;">#ifdef __cplusplus</span><br /><span style="color: #009900; margin: 0px; padding: 0px;">}</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#endif</span><br /><span style="color: #339933; margin: 0px; padding: 0px;">#endif</span></pre></td></tr></tbody></table></div><div style="background-color: #3b5998; font-family: Tahoma, Arial, Helvetica, sans-serif; font-size: 13px; line-height: 14pt; padding: 5px 0px; text-align: justify;">The C++ implementation file SortArray.cpp will be:</div><div class="wp_syntax" style="background-color: #f9f9f9; border: 1px solid silver; color: #110000; font-family: Arial, Helvetica, sans-serif; font-size: 13px; margin: 0px 0px 1.5em; overflow-x: auto; overflow-y: hidden; padding: 0px; width: 3305.609375px;"><table style="border-collapse: collapse !important; border: none !important; margin: 0px !important; padding: 0px !important; width: 3305px;"><tbody style="margin: 0px; padding: 0px;"><tr style="margin: 0px; padding: 0px;"><td class="line_numbers" style="border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important;"><pre style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: rgb(221, 238, 255) !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; color: gray !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; text-align: right !important; width: 16px !important;">1<br />2<br />3<br />4<br />5<br />6<br />7<br />8<br />9<br />10<br />11<br />12<br />13<br />14<br />15<br />16<br />17<br />18<br />19<br />20<br />21<br />22<br />23<br />24<br />25<br />26<br />27<br />28<br />29<br />30<br />31<br />32<br /></pre></td><td class="code" style="background-color: #eeeeee; background-image: linear-gradient(transparent 50%, rgba(255, 255, 255, 0.901961) 50%); background-size: 1px 32px; border: none !important; margin: 0px; padding: 0px !important; vertical-align: top !important; width: 3281px;"><pre class="cpp" style="-webkit-box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; background-color: transparent !important; border-bottom-left-radius: 0px !important; border-bottom-right-radius: 0px !important; border-top-left-radius: 0px !important; border-top-right-radius: 0px !important; border: none !important; box-shadow: rgba(0, 0, 0, 0) 0px 0px 0px !important; clear: none !important; float: none !important; font-size: 12px !important; line-height: 16px !important; overflow: visible !important; padding: 0px 4px !important; width: auto !important;"><span style="color: #339900; margin: 0px; padding: 0px;">#include "SortArray.h"</span><br /><span style="color: #339900; margin: 0px; padding: 0px;">#include "jni.h"</span><br /> <br /><span style="color: red; font-style: italic; margin: 0px; padding: 0px;">/*<br /> * Class: SortArray<br /> * Method: sort<br /> * Signature: ([I)[I<br /> */</span><br />JNIEXPORT jintArray JNICALL Java_SortArray_sort<br /> <span style="color: green; margin: 0px; padding: 0px;">(</span>JNIEnv <span style="color: #000040; margin: 0px; padding: 0px;">*</span>env, jobject obj, jintArray arr<span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: green; margin: 0px; padding: 0px;">{</span><br /> <br /> jsize arrLength <span style="color: navy; margin: 0px; padding: 0px;">=</span> env<span style="color: #000040; margin: 0px; padding: 0px;">-</span><span style="color: navy; margin: 0px; padding: 0px;">></span>GetArrayLength<span style="color: green; margin: 0px; padding: 0px;">(</span>arr<span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> jintArray arrSorted <span style="color: navy; margin: 0px; padding: 0px;">=</span> env<span style="color: #000040; margin: 0px; padding: 0px;">-</span><span style="color: navy; margin: 0px; padding: 0px;">></span>NewIntArray<span style="color: green; margin: 0px; padding: 0px;">(</span>arrLength<span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: teal; margin: 0px; padding: 0px;">;</span> <br /> <br /> jint <span style="color: #000040; margin: 0px; padding: 0px;">*</span>arrOut <span style="color: navy; margin: 0px; padding: 0px;">=</span> <span style="color: blue; margin: 0px; padding: 0px;">NULL</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> arrOut <span style="color: navy; margin: 0px; padding: 0px;">=</span> env<span style="color: #000040; margin: 0px; padding: 0px;">-</span><span style="color: navy; margin: 0px; padding: 0px;">></span>GetIntArrayElements<span style="color: green; margin: 0px; padding: 0px;">(</span>arr, <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> <br /> <span style="color: blue; margin: 0px; padding: 0px;">for</span><span style="color: green; margin: 0px; padding: 0px;">(</span>jsize x <span style="color: navy; margin: 0px; padding: 0px;">=</span> <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: teal; margin: 0px; padding: 0px;">;</span> x <span style="color: navy; margin: 0px; padding: 0px;"><</span> arrLength<span style="color: teal; margin: 0px; padding: 0px;">;</span> x<span style="color: #000040; margin: 0px; padding: 0px;">++</span><span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: green; margin: 0px; padding: 0px;">{</span><br /> <span style="color: blue; margin: 0px; padding: 0px;">for</span><span style="color: green; margin: 0px; padding: 0px;">(</span>jsize y <span style="color: navy; margin: 0px; padding: 0px;">=</span> <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: teal; margin: 0px; padding: 0px;">;</span> y <span style="color: navy; margin: 0px; padding: 0px;"><</span> arrLength <span style="color: #000040; margin: 0px; padding: 0px;">-</span> <span style="color: #0000dd; margin: 0px; padding: 0px;">1</span><span style="color: teal; margin: 0px; padding: 0px;">;</span> y<span style="color: #000040; margin: 0px; padding: 0px;">++</span><span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: green; margin: 0px; padding: 0px;">{</span><br /> <span style="color: blue; margin: 0px; padding: 0px;">if</span><span style="color: green; margin: 0px; padding: 0px;">(</span>arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: green; margin: 0px; padding: 0px;">]</span> <span style="color: navy; margin: 0px; padding: 0px;">></span> arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: #000040; margin: 0px; padding: 0px;">+</span><span style="color: #0000dd; margin: 0px; padding: 0px;">1</span><span style="color: green; margin: 0px; padding: 0px;">]</span><span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: green; margin: 0px; padding: 0px;">{</span><br /> jsize temp <span style="color: navy; margin: 0px; padding: 0px;">=</span> arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: #000040; margin: 0px; padding: 0px;">+</span><span style="color: #0000dd; margin: 0px; padding: 0px;">1</span><span style="color: green; margin: 0px; padding: 0px;">]</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: #000040; margin: 0px; padding: 0px;">+</span><span style="color: #0000dd; margin: 0px; padding: 0px;">1</span><span style="color: green; margin: 0px; padding: 0px;">]</span> <span style="color: navy; margin: 0px; padding: 0px;">=</span> arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: green; margin: 0px; padding: 0px;">]</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> arrOut<span style="color: green; margin: 0px; padding: 0px;">[</span>y<span style="color: green; margin: 0px; padding: 0px;">]</span> <span style="color: navy; margin: 0px; padding: 0px;">=</span> temp<span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> <span style="color: green; margin: 0px; padding: 0px;">}</span><br /> <span style="color: green; margin: 0px; padding: 0px;">}</span><br /> <span style="color: green; margin: 0px; padding: 0px;">}</span><br /> <br /> env<span style="color: #000040; margin: 0px; padding: 0px;">-</span><span style="color: navy; margin: 0px; padding: 0px;">></span>SetIntArrayRegion<span style="color: green; margin: 0px; padding: 0px;">(</span>arrSorted, <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span>, arrLength, arrOut<span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> env<span style="color: #000040; margin: 0px; padding: 0px;">-</span><span style="color: navy; margin: 0px; padding: 0px;">></span>ReleaseIntArrayElements<span style="color: green; margin: 0px; padding: 0px;">(</span>arr, arrOut, <span style="color: #0000dd; margin: 0px; padding: 0px;">0</span><span style="color: green; margin: 0px; padding: 0px;">)</span><span style="color: teal; margin: 0px; padding: 0px;">;</span><br /> <br /> <span style="color: blue; margin: 0px; padding: 0px;">return</span> arrSorted<span style="color: teal; margin: 0px; padding: 0px;">;</span><br /><span style="color: green; margin: 0px; padding: 0px;">}</span></pre></td></tr></tbody></table></div>

1 2 3 4 5 6 7 8 9 JNIExport jint JNICALL Java_IntArray_sumArray ( JNIEnv * env , jobject obj , jintArray arr ) { jsize len = * env -...

[Android NDK] Returning String array from C program to Java(JNI)

<div><span style="color: #5c5c5c; font-family: Courier New, Courier, mono, serif;"><span style="font-size: 12px; line-height: 14px;"> </span><span style="line-height: 14px;">Returning String array from C program to Java</span></span></div><div><br /></div><div><span style="color: #5c5c5c; font-family: Courier New, Courier, mono, serif;"><span style="font-size: 12px; line-height: 14px;"><br /></span></span></div><div><ol class="dp-j" start="1" style="background-color: white; border: none; color: #5c5c5c; font-family: 'Courier New', Courier, mono, serif; font-size: 12px; line-height: 18px; list-style-image: initial; list-style-position: initial; margin: 0px 0px 1px 45px !important; padding: 0px;"><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;"><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">#include <jni.h>  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">  #include <span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"ArrayHandler.h"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">  </span></span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">   </span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">  JNIEXPORT jobjectArray JNICALL   </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">               Java_ArrayHandler_returnArray  </span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">  (JNIEnv *env, jobject jobj){  </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">   </span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    jobjectArray ret;  </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    <span class="keyword" style="background-color: inherit; border: none; color: #006699; font-weight: bold; margin: 0px; padding: 0px;">int</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;"> i;  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">   </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    <span class="keyword" style="background-color: inherit; border: none; color: #006699; font-weight: bold; margin: 0px; padding: 0px;">char</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;"> *message[</span><span class="number" style="background-color: inherit; border: none; color: #c00000; margin: 0px; padding: 0px;">5</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">]= {</span><span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"first"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">,   </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;"><span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"second"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">,   </span></span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;"><span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"third"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">,   </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;"><span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"fourth"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">,   </span></span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;"><span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"fifth"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">};  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">   </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    ret= (jobjectArray)env->NewObjectArray(<span class="number" style="background-color: inherit; border: none; color: #c00000; margin: 0px; padding: 0px;">5</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">,  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">         env->FindClass(<span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">"java/lang/String"</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">),  </span></span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">         env->NewStringUTF(<span class="string" style="background-color: inherit; border: none; color: blue; margin: 0px; padding: 0px;">""</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">));  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">   </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    <span class="keyword" style="background-color: inherit; border: none; color: #006699; font-weight: bold; margin: 0px; padding: 0px;">for</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">(i=</span><span class="number" style="background-color: inherit; border: none; color: #c00000; margin: 0px; padding: 0px;">0</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">;i<</span><span class="number" style="background-color: inherit; border: none; color: #c00000; margin: 0px; padding: 0px;">5</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">;i++) {  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">        env->SetObjectArrayElement(  </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">ret,i,env->NewStringUTF(message[i]));  </span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    }  </span></li><li class="alt" style="background-color: #eadbc4; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; color: inherit; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">    <span class="keyword" style="background-color: inherit; border: none; color: #006699; font-weight: bold; margin: 0px; padding: 0px;">return</span><span style="background-color: inherit; border: none; margin: 0px; padding: 0px;">(ret);  </span></span></li><li class="" style="background-color: #f0e6d5; border-left-color: rgb(222, 199, 164); border-left-width: 3px; border-style: none none none solid; line-height: 14px; list-style: decimal-leading-zero outside; margin: 0px !important; padding: 0px 3px 0px 10px !important;"><span style="background-color: inherit; border: none; color: black; margin: 0px; padding: 0px;">  }  </span></li></ol></div>

  Returning String array from C program to Java #include <jni.h>     #include  "ArrayHandler.h"          JNIEXPORT jobjectAr...

[Android NDK ] Basic Procedure

<h1 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: x-large; margin-top: 0px; max-width: 700px; padding-left: 0px;"><span style="font-size: 13px; line-height: 1.25em;">The steps that you have to take to develop JNI libraries for Android phones are simple in principle. They are outlined below.</span></h1><ul style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">Install the JNI/NDK package from Google</li><li style="margin-bottom: 0.3em;">Create your Android project</li><li style="margin-bottom: 0.3em;">Make a JNI folder in your Android project root directory (called 'jni')</li><li style="margin-bottom: 0.3em;">Put your JNI sources in the 'jni' folder</li><li style="margin-bottom: 0.3em;">Create an 'Android.mk' file, and place it in the 'jni' folder</li><li style="margin-bottom: 0.3em;">Optionally create an 'Application.mk' file, and place it in the 'jni' folder</li><li style="margin-bottom: 0.3em;">Open a command line terminal and navigate to the root directory of your Android project.</li><li style="margin-bottom: 0.3em;">Execute 'ndk-build', (if it's in your PATH variable) or execute '/path/to/command/ndk-build'</li><li style="margin-bottom: 0.3em;">The 'ndk-build' command creates the binary for your library and puts it in the proper folder.</li><li style="margin-bottom: 0.3em;">Switch to Eclipse, Refresh the 'Project Explorer View' (F5)</li><li style="margin-bottom: 0.3em;">Rebuild the project</li><li style="margin-bottom: 0.3em;">Run your project testing your JNI library.</li></ul><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The tutorial will now attempt to go through these steps. We will skip the 'Install the JNI/NDK' step as it's already been covered. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Create_Android_Project"></a>Create Android Project</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This step entails using Eclipse to create a new Android project. This project will have a folder in the Eclipse 'workspace' directory. The location of the 'workspace' directory and the project directory inside it should be known to you. The 'project' directory name is the name of your project to eclipse.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">On a linux system the 'workspace' directory is commonly located in the user's home directory. The project is inside it. When this or other documentation refers to the project's root, for a project named 'projectname', they would be referring to the following path.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">/home/myname/workspace/projectname/</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This is important for steps where you create the 'jni' folder and where you call the 'ndk-build' script. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Make_JNI_Folder"></a>Make JNI Folder</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">A folder named 'jni' (lowercase) must be created by you in the Eclipse project's root directory. In a linux system where the user is called 'myname' and the project is called 'projectname', this folder would be located in the 'projectname' folder, as referred to by the following path.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">/home/myname/workspace/projectname/jni/</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This would place a folder at the same level as the Eclipse/Java 'bin', 'src', and 'res' folders. It would also be at the same level as the 'AndroidManifest.xml' file. Inside this folder is where the source c or c++ documents need to be placed.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">If you use Eclipse to create this folder, then you are done with this step. If you create the folder from the command line, don't forget to type F5 or click on 'Refresh' to let Eclipse register that there has been a change to the folder structure. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="JNI_Sources"></a>JNI Sources</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Here you work on the actual source files in c or c++. You will probably return to this step many times as your JNI library evolves. A large part of this how-to is focused on showing how c can be used to create a simple JNI library like the one used in the Awesomeguy program.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This document will explain the creation of a JNI library consisting of a single source file. Choose a name for your file and place it in the 'jni' folder. For this document the library will be called 'example' so the file will be called 'example.c'. On a linux system the path to the 'example.c' file will look something like the path shown below.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">/home/myname/workspace/projectname/jni/example.c</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">After placing the file 'example.c' in the 'jni' folder you should refresh Eclipse so that it recognizes the new file. The file 'example.c' should be a simple text file. To edit the file you need a regular text editor. On linux systems, when viewing the project from Eclipse, if you double click on the file 'example.c' in the Project Explorer view, the system's text editor is automatically opened with 'example.c' loaded. You can then make changes and save and re-compile the source code. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Create_Android_mk_File"></a>Create Android mk File</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Before the NDK build tools will compile your code they need a 'Makefile' file. That's the purpose of the file 'Android.mk'. Because our project only uses a single source file for the JNI library, our 'Android.mk' file will be simple to write. Information on writing the 'Android.mk' file can be found in the 'docs' folder inside the 'android-ndk-r4b' folder. The most relevant document is the 'ANDROID-MK.TXT', and this document does a thorough job of explaining the parts of the file that are required.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">An example 'Android.mk' file is shown below. This file is taken from the Awesomeguy project.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">LOCAL_PATH</span><span class="pun" style="color: #666600;">:=</span><span class="pln"> $</span><span class="pun" style="color: #666600;">(</span><span class="pln">call </span><span class="kwd" style="color: #000088;">my</span><span class="pun" style="color: #666600;">-</span><span class="pln">dir</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">CLEAR_VARS</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />LOCAL_MODULE    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> awesomeguy<br />LOCAL_CFLAGS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="typ" style="color: #660066;">Werror</span><span class="pln"><br />LOCAL_SRC_FILES </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> awesomeguy</span><span class="pun" style="color: #666600;">.</span><span class="pln">c<br />LOCAL_LDLIBS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="pln">llog <br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">BUILD_SHARED_LIBRARY</span><span class="pun" style="color: #666600;">)</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">For the purposes of this tutorial we'll leave most of the file as it is.</div><ul style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">LOCAL_PATH - this line should be left as it is since your source file ('example.c') is in the same directory as the 'Android.mk' file.</li><li style="margin-bottom: 0.3em;">include $(CLEAR_VARS) - this line should be left as it is. It is required.</li><li style="margin-bottom: 0.3em;">LOCAL_MODULE - this line should be changed to match your module name. For this tutorial we'll change it to 'example'. This name should not have any spaces in it as it will be made into the actual library's name ('libexample.so' for us).</li><li style="margin-bottom: 0.3em;">LOCAL_CFLAGS - This line can be left as it is. It is for compiler flags.</li><li style="margin-bottom: 0.3em;">LOCAL_SRC_FILES - this line should be changed to 'example.c' since that's our source file.</li><li style="margin-bottom: 0.3em;">LOCAL_LDLIBS - leave this the same.</li><li style="margin-bottom: 0.3em;">include $(BUILD_SHARED_LIBRARY) - leave this the same.</li></ul><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">So our new 'Android.mk' file should look like this.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">LOCAL_PATH</span><span class="pun" style="color: #666600;">:=</span><span class="pln"> $</span><span class="pun" style="color: #666600;">(</span><span class="pln">call </span><span class="kwd" style="color: #000088;">my</span><span class="pun" style="color: #666600;">-</span><span class="pln">dir</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">CLEAR_VARS</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />LOCAL_MODULE    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> example<br />LOCAL_CFLAGS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="typ" style="color: #660066;">Werror</span><span class="pln"><br />LOCAL_SRC_FILES </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> example</span><span class="pun" style="color: #666600;">.</span><span class="pln">c<br />LOCAL_LDLIBS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="pln">llog <br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">BUILD_SHARED_LIBRARY</span><span class="pun" style="color: #666600;">)</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The NDK build tools will compile the code, and then if there are no errors it will name the object code 'libexample.so' and place it in the Android project in a new folder that it creates especially for this purpose. The name of the folder is '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">libs/armeabi/</tt>'. The build tools also manage the creation of some other files that are necessary.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The name, 'libexample.so' comes from the 'LOCAL_MODULE' line in the 'Android.mk' file, and it is the library name, but when referring to the module in the java code you refer to 'example' not 'libexample.so'. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Go_To_Project_Root"></a>Go To Project Root</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The project root is the base folder for the Eclipse Android project. It's found in the 'workspace' directory. It is <i>not</i> the 'jni' folder, but instead its parent. Using the conventions we've been following for linux systems, the path to the project root directory would be the following.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">/home/myname/workspace/projectname/</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">You want to 'cd' into this directory from the command line. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Execute_Build_Command"></a>Execute Build Command</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The command to start the build scripts is called 'ndk-build'. The script for 'ndk-build' is located in the Android NDK package of software that you already downloaded. If you followed the tutorial so far, you would have placed the 'android-ndk-r4b' folder in your 'bin' directory, and then you would have added it to your path. If this is the case, simply type 'ndk-build' at the command line.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">If you didn't put the 'android-ndk-r4b' folder in your PATH variable in the '.bashrc' file, then you can explicitly specify the path to the 'ndk-build' script when you invoke it. The command for this is shown below. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">/home/myname/bin/android-ndk-r4b/ndk-build</tt></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="What_Build_Command_Does"></a>What Build Command Does</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The ndk-build script compiles the source code for the Android project and places it in a directory where it can be included by the Eclipse build function in the final apk file.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The folder where the resulting binary library goes is the '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">libs/armeabi/</tt>' folder. Two other files are placed in that folder along with the JNI library that we are creating. They are created automatically, so we're not going to worry about them. One is the 'gdb.setup' file, and one is the 'gdbserver' file. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Refresh_Project_Explorer_View"></a>Refresh Project Explorer View</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The 'Project Explorer' is one of the Eclipse windows that is visible when doing standard editing on the default Java perspective. It is commonly on the left side of the Eclipse screen. It shows all the files and folders in a project. You can refresh the view by selecting a project and then pressing the <tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;"><F5></tt> key, or by right clicking on the project name and selecting 'Refresh' from the menu that is displayed. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Rebuild_Project"></a>Rebuild Project</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Like refreshing the project, you can rebuild the project by right clicking on the project name in the Project Explorer and then selecting 'Build Project' from the menu that's displayed. Some activities, like the 'Run' activity, automatically rebuild the project when the Eclipse IDE sees that the project has changed. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Test_Project"></a>Test Project</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Test your project thoroughly. This step goes without saying.</div><h1 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: x-large; margin-top: 0px; max-width: 700px; padding-left: 0px;"><a href="https://www.blogger.com/null" name="Writing_JNI_Sources"></a>Writing JNI Sources</h1><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">For our purposes here we want to build a JNI library from a single c source file. It is possible to use c++ and several source files, but we're not going to do that.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">We need to be able to write methods that can be called in java code. We need to be able to pass variables to the library and pass variables from the library to java.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">We will assume that the JNI library that we're using is called 'libexample.so', and that the module name, as defined in the 'Android.mk' file is 'example'. We'll also assume that the package name for the Android project we're working on is something simple. We'll use this.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">org.testjni.android</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This means you have a line in your program files that looks like this.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="kwd" style="color: #000088;">package</span><span class="pln"> org</span><span class="pun" style="color: #666600;">.</span><span class="pln">testjni</span><span class="pun" style="color: #666600;">.</span><span class="pln">android</span><span class="pun" style="color: #666600;">;</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">It also means that there is a file folder structure in your Eclipse project under 'src' that looks like this.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"><tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">src/org/testjni/android/</tt></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">We'll assume that the Java file that we want to call the JNI from is called 'Game.java'.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">In your JNI library source file you must '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">#include</tt>' the library 'jni.h'. Including the library would look like this. Including this library ensures that the source file you are working on will compile.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="com" style="color: #880000;">#include</span><span class="pln"> </span><span class="str" style="color: #008800;"><jni.h></span></pre><blockquote style="font-family: arial, sans-serif; font-size: 13px; margin: 20px; max-width: 60em;"><a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></blockquote><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Naming_Functions"></a>Naming Functions</h3><h4 style="font-family: arial, sans-serif; font-size: 13px;"><a href="https://www.blogger.com/null" name="Example_One"></a>Example One</h4><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The naming conventions for these methods are fairly complex. The average JNI native function name is unwieldy and looks something like this:</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">JNIEXPORT </span><span class="kwd" style="color: #000088;">void</span><span class="pln"> JNICALL </span><span class="typ" style="color: #660066;">Java_org_testjni_android_Game_someFunction</span><span class="pun" style="color: #666600;">(</span><span class="typ" style="color: #660066;">JNIEnv</span><span class="pln"> </span><span class="pun" style="color: #666600;">*</span><span class="pln"> env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jobject  obj</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">{}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">In this example the method body is empty. The java native method 'someFunction()' would call the c function above. The name for this c function can be broken down into parts. The first part is the information before the method name. This is listed below.</div><ol style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">the macro JNIEXPORT</li><li style="margin-bottom: 0.3em;">the return type for the method ('void' in this example)</li><li style="margin-bottom: 0.3em;">the macro JNICALL</li></ol><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">After that comes the actual name of the method. The name can be broken down into parts. They are listed below. The parts are separated by underscores.</div><ol style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">the text '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">Java_</tt>'</li><li style="margin-bottom: 0.3em;">the text for the package name of the Android app, with the periods replaced by underscores</li><li style="margin-bottom: 0.3em;">the name of the class that the function will be part of</li><li style="margin-bottom: 0.3em;">the name of the function</li></ol><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;"></div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This is followed by the two mandatory parameters '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">JNIEnv * env</tt>' and '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jobject obj</tt>'. Other parameters for the function could have followed the mandatory ones listed above. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h4 style="font-family: arial, sans-serif; font-size: 13px;"><a href="https://www.blogger.com/null" name="Example_Two"></a>Example Two</h4><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">JNIEXPORT </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> JNICALL </span><span class="typ" style="color: #660066;">Java_org_testjni_android_Game_someFunction</span><span class="pun" style="color: #666600;">(</span><span class="typ" style="color: #660066;">JNIEnv</span><span class="pln"> </span><span class="pun" style="color: #666600;">*</span><span class="pln"> env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jobject  obj</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">{</span><span class="pln"><br /></span><span class="kwd" style="color: #000088;">return</span><span class="pln"> </span><span class="lit" style="color: #006666;">3</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">In this example the method body is the 'return' statement that returns the number 3. The java native method 'someFunction()' would call the c function above. Note that the return type is 'int' not 'void'. This is as you would expect from a c function. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h4 style="font-family: arial, sans-serif; font-size: 13px;"><a href="https://www.blogger.com/null" name="Example_Three"></a>Example Three</h4><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">JNIEXPORT </span><span class="kwd" style="color: #000088;">void</span><span class="pln"> JNICALL </span><span class="typ" style="color: #660066;">Java_org_testjni_android_Game_someFunction</span><span class="pun" style="color: #666600;">(</span><span class="typ" style="color: #660066;">JNIEnv</span><span class="pln"> </span><span class="pun" style="color: #666600;">*</span><span class="pln"> env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jobject  obj</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jint x</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">{</span><span class="pln"><br /></span><span class="kwd" style="color: #000088;">int</span><span class="pln"> xx </span><span class="pun" style="color: #666600;">=</span><span class="pln"> x</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br /></span><span class="kwd" style="color: #000088;">return</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">In this example the method body is not empty, but performs only a trivial task. The java native method 'someFunction(int x)' would call the c function above. In all examples the first two parameters to the c function are mandatory. The variables '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">JNIEnv * env</tt>' and '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jobject obj</tt>' are included in all functions that are going to be called from the java code.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">NOTE: You must '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">#include</tt>' the library '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jni.h</tt>' at the beginning of your source file for these functions to compile right. That would look like this. Do not forget this step.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="com" style="color: #880000;">#include</span><span class="pln"> </span><span class="str" style="color: #008800;"><jni.h></span></pre><blockquote style="font-family: arial, sans-serif; font-size: 13px; margin: 20px; max-width: 60em;"><a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></blockquote><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Java_Declaration"></a>Java Declaration</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">There are two parts to the java declaration for the example code that we are using for this explanation. One part loads the library, and another part makes reference to the method so that the other java code in the app can call it. The declaration looks like the code below.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="kwd" style="color: #000088;">static</span><span class="pln"> </span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />        </span><span class="typ" style="color: #660066;">System</span><span class="pun" style="color: #666600;">.</span><span class="pln">loadLibrary</span><span class="pun" style="color: #666600;">(</span><span class="str" style="color: #008800;">"example"</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This code has to be included in the Java class where the JNI is to be used. The second part of the java listing would look as follows.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="kwd" style="color: #000088;">public</span><span class="pln"> </span><span class="kwd" style="color: #000088;">native</span><span class="pln"> </span><span class="kwd" style="color: #000088;">void</span><span class="pln"> someFunction</span><span class="pun" style="color: #666600;">();</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">This line of code is like a java method declaration <i>without</i> the body. This function is also 'public' so it can be called by methods of other classes if they have an instantiated version of the class 'Game'.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">You should note that the c method declaration is different from the java declaration, but you need both, and the c version must include the package name and the java class name. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><a href="https://www.blogger.com/null" name="Passing_Arrays"></a>Passing Arrays</h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">One thing that was essential in the awesomeguy.c file was the passing of arrays between the JNI code and the Java code. In awesomeguy the bitmaps for the main character and the other graphic elements were converted to arrays in the java code and then passed to the JNI library during the class instantiation phase. When it was time to draw the actual screen, the JNI code assembled a large array that was passed back to the java code. In java the array was converted to a bitmap and displayed on the screen. <a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></div><h4 style="font-family: arial, sans-serif; font-size: 13px;"><a href="https://www.blogger.com/null" name="Arrays_as_Parameter"></a>Arrays as Parameter</h4><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Here is an example of code actually used in the awesomeguy.c JNI file. It shows how a '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jintArray</tt>', which is an array of integers, can be passed to a JNI library. It also shows the processing that's needed to access the data in the manner of a c int array.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Note that the first two parameters to the JNI method are always the same. They are '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">JNIEnv * env</tt>, and <tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jobject obj</tt>'. After that the method can be customized in different ways.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">JNIEXPORT </span><span class="kwd" style="color: #000088;">void</span><span class="pln"> JNICALL</span><span class="typ" style="color: #660066;">Java_org_davidliebman_android_awesomeguy_Panel_setTileMapData</span><span class="pun" style="color: #666600;">(</span><span class="typ" style="color: #660066;">JNIEnv</span><span class="pln"> </span><span class="pun" style="color: #666600;">*</span><span class="pln"> env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jobject  obj</span><span class="pun" style="color: #666600;">,</span><span class="pln"><br />jintArray a_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jintArray b_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jintArray c_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jintArray d_bitmap</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />  </span><span class="com" style="color: #880000;">//jsize a_len = (*env)->GetArrayLength(env, a_bitmap);</span><span class="pln"><br />  jint </span><span class="pun" style="color: #666600;">*</span><span class="pln">a </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">GetIntArrayElements</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> a_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />  </span><span class="com" style="color: #880000;">//jsize b_len = (*env)->GetArrayLength(env, b_bitmap);</span><span class="pln"><br />  jint </span><span class="pun" style="color: #666600;">*</span><span class="pln">b </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">GetIntArrayElements</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> b_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />  </span><span class="com" style="color: #880000;">//jsize c_len = (*env)->GetArrayLength(env, c_bitmap);</span><span class="pln"><br />  jint </span><span class="pun" style="color: #666600;">*</span><span class="pln">c </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">GetIntArrayElements</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> c_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />  </span><span class="com" style="color: #880000;">//jsize d_len = (*env)->GetArrayLength(env, d_bitmap);</span><span class="pln"><br />  jint </span><span class="pun" style="color: #666600;">*</span><span class="pln">d </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">GetIntArrayElements</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> d_bitmap</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />  setTileMapData</span><span class="pun" style="color: #666600;">(</span><span class="pln">a</span><span class="pun" style="color: #666600;">,</span><span class="pln"> b</span><span class="pun" style="color: #666600;">,</span><span class="pln"> c</span><span class="pun" style="color: #666600;">,</span><span class="pln"> d </span><span class="pun" style="color: #666600;">);</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">There are lines in the above code that are purposely commented out. They demonstrate how to determine the size of the array that has been passed to the JNI library. In our program, we know the size of the arrays. We rely on the fact that the arrays are a given size representing their visual size when displayed on the screen.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">There are three important aspects of the method above. They're listed below. For this explanation we'll focus on '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">a_bitmap</tt>'.</div><ol style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">The parameters in the function signature call for 'jintArray' elements to be passed to the method.</li><li style="margin-bottom: 0.3em;">The size of the 'jintArray' is determined by the line: '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jsize a_len = (*env)->GetArrayLength(env, a_bitmap);</tt>'</li><li style="margin-bottom: 0.3em;">The actual array pointer to be used in c style code is found like this: '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jint *a = (*env)->GetIntArrayElements(env, a_bitmap, 0);</tt>'</li></ol><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The Java code that allows us to use this method is:</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="kwd" style="color: #000088;">public</span><span class="pln"> </span><span class="kwd" style="color: #000088;">native</span><span class="pln"> </span><span class="kwd" style="color: #000088;">void</span><span class="pln"> setTileMapData</span><span class="pun" style="color: #666600;">(</span><span class="pln"> </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> </span><span class="pun" style="color: #666600;">[]</span><span class="pln"> a</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> </span><span class="pun" style="color: #666600;">[]</span><span class="pln"> b</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> </span><span class="pun" style="color: #666600;">[]</span><span class="pln"> c</span><span class="pun" style="color: #666600;">,</span><span class="pln"> </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> </span><span class="pun" style="color: #666600;">[]</span><span class="pln"> d</span><span class="pun" style="color: #666600;">);</span></pre><blockquote style="font-family: arial, sans-serif; font-size: 13px; margin: 20px; max-width: 60em;"><a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></blockquote><h4 style="font-family: arial, sans-serif; font-size: 13px;"><a href="https://www.blogger.com/null" name="Arrays_as_Return_Type"></a>Arrays as Return Type</h4><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">Arrays can be returned to the Java code from the JNI library. The process is involved. Below is a block of code from the Awesomeguy JNI library where we pass an integer to the method and return an entire array from the method.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">JNIEXPORT jintArray JNICALL</span><span class="typ" style="color: #660066;">Java_org_davidliebman_android_awesomeguy_Panel_drawLevel</span><span class="pun" style="color: #666600;">(</span><span class="typ" style="color: #660066;">JNIEnv</span><span class="pln"> </span><span class="pun" style="color: #666600;">*</span><span class="pln"> env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> jobject  obj</span><span class="pun" style="color: #666600;">,</span><span class="pln"><br />jint animate</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />        </span><span class="kwd" style="color: #000088;">int</span><span class="pln"> j</span><span class="pun" style="color: #666600;">,</span><span class="pln">k</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br />        jint size </span><span class="pun" style="color: #666600;">=</span><span class="pln"> SCREEN_WIDTH </span><span class="pun" style="color: #666600;">*</span><span class="pln"> SCREEN_HEIGHT</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br />        jint fill</span><span class="pun" style="color: #666600;">[</span><span class="pln">size</span><span class="pun" style="color: #666600;">];</span><span class="pln"> <br />        jintArray graphic</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br />        drawLevel</span><span class="pun" style="color: #666600;">(</span><span class="pln">animate</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />        graphic </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">NewIntArray</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> size</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />        </span><span class="kwd" style="color: #000088;">if</span><span class="pun" style="color: #666600;">(</span><span class="pln">graphic </span><span class="pun" style="color: #666600;">==</span><span class="pln"> NULL</span><span class="pun" style="color: #666600;">)</span><span class="pln"> </span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />                LOGE</span><span class="pun" style="color: #666600;">(</span><span class="str" style="color: #008800;">"ARRAY NOT CREATED"</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />                </span><span class="kwd" style="color: #000088;">return</span><span class="pln"> NULL</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br />        </span><span class="pun" style="color: #666600;">}</span><span class="pln"><br />        </span><span class="kwd" style="color: #000088;">for</span><span class="pln"> </span><span class="pun" style="color: #666600;">(</span><span class="pln">j </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">;</span><span class="pln"> j </span><span class="pun" style="color: #666600;"><</span><span class="pln"> SCREEN_HEIGHT</span><span class="pun" style="color: #666600;">;</span><span class="pln"> j</span><span class="pun" style="color: #666600;">++)</span><span class="pln"> </span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />                </span><span class="kwd" style="color: #000088;">for</span><span class="pln"> </span><span class="pun" style="color: #666600;">(</span><span class="pln">k </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">;</span><span class="pln"> k </span><span class="pun" style="color: #666600;"><</span><span class="pln"> SCREEN_WIDTH </span><span class="pun" style="color: #666600;">;</span><span class="pln"> k </span><span class="pun" style="color: #666600;">++</span><span class="pln"> </span><span class="pun" style="color: #666600;">)</span><span class="pln"> </span><span class="pun" style="color: #666600;">{</span><span class="pln"><br />                        fill</span><span class="pun" style="color: #666600;">[</span><span class="pln"> </span><span class="pun" style="color: #666600;">(</span><span class="pln">j </span><span class="pun" style="color: #666600;">*</span><span class="pln"> SCREEN_WIDTH</span><span class="pun" style="color: #666600;">)</span><span class="pln"> </span><span class="pun" style="color: #666600;">+</span><span class="pln"> k </span><span class="pun" style="color: #666600;">]</span><span class="pln"> </span><span class="pun" style="color: #666600;">=</span><span class="pln"> </span><span class="pun" style="color: #666600;">(</span><span class="pln">jint</span><span class="pun" style="color: #666600;">)</span><span class="pln"> screen</span><span class="pun" style="color: #666600;">[</span><span class="pln">j</span><span class="pun" style="color: #666600;">][</span><span class="pln">k</span><span class="pun" style="color: #666600;">];</span><span class="pln"><br />                </span><span class="pun" style="color: #666600;">}</span><span class="pln"><br />        </span><span class="pun" style="color: #666600;">}</span><span class="pln"><br />        <br />        <br />        </span><span class="pun" style="color: #666600;">(*</span><span class="pln">env</span><span class="pun" style="color: #666600;">)-></span><span class="typ" style="color: #660066;">SetIntArrayRegion</span><span class="pun" style="color: #666600;">(</span><span class="pln">env</span><span class="pun" style="color: #666600;">,</span><span class="pln"> graphic</span><span class="pun" style="color: #666600;">,</span><span class="lit" style="color: #006666;">0</span><span class="pun" style="color: #666600;">,</span><span class="pln"> size</span><span class="pun" style="color: #666600;">,</span><span class="pln"> fill</span><span class="pun" style="color: #666600;">);</span><span class="pln"><br />        </span><span class="kwd" style="color: #000088;">return</span><span class="pln"> graphic</span><span class="pun" style="color: #666600;">;</span><span class="pln"><br /></span><span class="pun" style="color: #666600;">}</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">We'll try to go over the code step by step.</div><ol style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">The first thing to notice is the '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jintArray</tt>' return type in the method signature.</li><li style="margin-bottom: 0.3em;">On the next line we pass a jint called 'animate' as a paramter.</li><li style="margin-bottom: 0.3em;">We declare two ints, 'j' and 'k' to be used as for() loop index variables.</li><li style="margin-bottom: 0.3em;">We declare a jint called 'size' that is the size of our array.</li><li style="margin-bottom: 0.3em;">We declare a c style array called <tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">fill[]</tt> that will hold our c data.</li><li style="margin-bottom: 0.3em;">We declare a special '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jintArray</tt>' called 'graphic'. This object still needs to be initialized.</li><li style="margin-bottom: 0.3em;">We call the method that will populate the 2D 'screen' array. This method calls all the necessary drawing functions of our library.</li><li style="margin-bottom: 0.3em;">We initialize the <tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">jintArray</tt> with a special JNI method that uses both the 'env' object and the 'size' jint that we defined previously.</li><li style="margin-bottom: 0.3em;">We test if the 'graphic' object was properly created. If not we return null.</li><li style="margin-bottom: 0.3em;">Using 'j' and 'k' we populate the 'fill' array. The 'fill' array is 1 dimensional and the 'screen' array is 2 dimensional.</li><li style="margin-bottom: 0.3em;">Using the special '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">SetIntArrayRegion()</tt>' method we place the 'fill' data in the 'graphic' object. The variables 'size' and 'env' are also used in this method call.</li><li style="margin-bottom: 0.3em;">We return the 'graphic' object.</li></ol><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">That covers the process we used to convert a c style array into a java array and pass it back to the java code. We only do this once in the entire library. Below is the code that must be included in the java to allow the JNI method to be called.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="kwd" style="color: #000088;">public</span><span class="pln"> </span><span class="kwd" style="color: #000088;">native</span><span class="pln"> </span><span class="kwd" style="color: #000088;">int</span><span class="pun" style="color: #666600;">[]</span><span class="pln"> drawLevel</span><span class="pun" style="color: #666600;">(</span><span class="kwd" style="color: #000088;">int</span><span class="pln"> num</span><span class="pun" style="color: #666600;">);</span></pre><blockquote style="font-family: arial, sans-serif; font-size: 13px; margin: 20px; max-width: 60em;"><a href="https://code.google.com/p/awesomeguy/wiki/JNITutorial#Introduction" style="color: #0000cc;">top</a></blockquote>

The steps that you have to take to develop JNI libraries for Android phones are simple in principle. They are outlined below. Install the JN...

[Android NDK ] Create Android mk File

<h3 style="background-image: none; border: 0px; font-family: arial, sans-serif; font-size: medium; margin: 0px; max-width: 700px; padding: 0.5ex 0.5em 0.5ex 0px;"><span style="font-size: 13px; line-height: 1.25em;">Before the NDK build tools will compile your code they need a 'Makefile' file. That's the purpose of the file 'Android.mk'. Because our project only uses a single source file for the JNI library, our 'Android.mk' file will be simple to write. Information on writing the 'Android.mk' file can be found in the 'docs' folder inside the 'android-ndk-r4b' folder. The most relevant document is the 'ANDROID-MK.TXT', and this document does a thorough job of explaining the parts of the file that are required.</span></h3><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">An example 'Android.mk' file is shown below. This file is taken from the Awesomeguy project.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">LOCAL_PATH</span><span class="pun" style="color: #666600;">:=</span><span class="pln"> $</span><span class="pun" style="color: #666600;">(</span><span class="pln">call </span><span class="kwd" style="color: #000088;">my</span><span class="pun" style="color: #666600;">-</span><span class="pln">dir</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">CLEAR_VARS</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />LOCAL_MODULE    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> awesomeguy<br />LOCAL_CFLAGS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="typ" style="color: #660066;">Werror</span><span class="pln"><br />LOCAL_SRC_FILES </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> awesomeguy</span><span class="pun" style="color: #666600;">.</span><span class="pln">c<br />LOCAL_LDLIBS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="pln">llog <br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">BUILD_SHARED_LIBRARY</span><span class="pun" style="color: #666600;">)</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">For the purposes of this tutorial we'll leave most of the file as it is.</div><ul style="font-family: arial, sans-serif; font-size: 13px; max-width: 62em; padding-left: 25px;"><li style="margin-bottom: 0.3em;">LOCAL_PATH - this line should be left as it is since your source file ('example.c') is in the same directory as the 'Android.mk' file.</li><li style="margin-bottom: 0.3em;">include $(CLEAR_VARS) - this line should be left as it is. It is required.</li><li style="margin-bottom: 0.3em;">LOCAL_MODULE - this line should be changed to match your module name. For this tutorial we'll change it to 'example'. This name should not have any spaces in it as it will be made into the actual library's name ('libexample.so' for us).</li><li style="margin-bottom: 0.3em;">LOCAL_CFLAGS - This line can be left as it is. It is for compiler flags.</li><li style="margin-bottom: 0.3em;">LOCAL_SRC_FILES - this line should be changed to 'example.c' since that's our source file.</li><li style="margin-bottom: 0.3em;">LOCAL_LDLIBS - leave this the same.</li><li style="margin-bottom: 0.3em;">include $(BUILD_SHARED_LIBRARY) - leave this the same.</li></ul><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">So our new 'Android.mk' file should look like this.</div><pre class="prettyprint" style="background-color: #eeeeee; font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 70em; overflow: auto; padding: 0.5em;"><span class="pln">LOCAL_PATH</span><span class="pun" style="color: #666600;">:=</span><span class="pln"> $</span><span class="pun" style="color: #666600;">(</span><span class="pln">call </span><span class="kwd" style="color: #000088;">my</span><span class="pun" style="color: #666600;">-</span><span class="pln">dir</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">CLEAR_VARS</span><span class="pun" style="color: #666600;">)</span><span class="pln"><br /><br />LOCAL_MODULE    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> example<br />LOCAL_CFLAGS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="typ" style="color: #660066;">Werror</span><span class="pln"><br />LOCAL_SRC_FILES </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> example</span><span class="pun" style="color: #666600;">.</span><span class="pln">c<br />LOCAL_LDLIBS    </span><span class="pun" style="color: #666600;">:=</span><span class="pln"> </span><span class="pun" style="color: #666600;">-</span><span class="pln">llog <br /><br />include $</span><span class="pun" style="color: #666600;">(</span><span class="pln">BUILD_SHARED_LIBRARY</span><span class="pun" style="color: #666600;">)</span></pre><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The NDK build tools will compile the code, and then if there are no errors it will name the object code 'libexample.so' and place it in the Android project in a new folder that it creates especially for this purpose. The name of the folder is '<tt style="font-family: Monaco, 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Lucida Console', monospace; font-size: 12px; max-width: 66em;">libs/armeabi/</tt>'. The build tools also manage the creation of some other files that are necessary.</div><div style="font-family: arial, sans-serif; font-size: 13px; line-height: 1.25em; max-width: 64em;">The name, 'libexample.so' comes from the 'LOCAL_MODULE' line in the 'Android.mk' file, and it is the library name, but when referring to the module in the java code you refer to 'example' not 'libexample.so'. </div>

Before the NDK build tools will compile your code they need a 'Makefile' file. That's the purpose of the file 'Android.mk...