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 <html>
 <head>
    <title>Beginning JNI with NetBeans IDE and C/C++ Plugin on Linux</title>
    <meta name="DESCRIPTION" content="A tutorial describing how to compile
 and run JNI powered Java applications using NetBeans IDE or Oracle Solaris Studio IDE.">
    <meta name="author" content="Susan Morgan"><!--Optional tag-->
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 <h1>Beginning JNI with NetBeans IDE and C/C++ Plugin on Linux</h1>
 <!-- START INTRO ---------------------------------------------------------------------------------------* -->
 <div class="articledate" style="margin-left: 0px;font-style:italic;">
  <!--  <p><em>Contributed by <i>Susan Morgan</i> <br> -->
  <em>March 2014</em> [Revision number: V8.0-1]</div>

 <p>This tutorial takes you through the creation of a simple application that
 uses Java<sup><small>TM</small></sup> Native Interface (JNI) code written in the C
 programming language.
 <p class="notes">The tutorial is specific to Linux.</p>
 <!-- END INTRO -->

 <h3>Contents</h3>
 <img src="../../../images_www/articles/74/netbeans-stamp-80-74.png" class="stamp"
 alt="Content on this page applies to NetBeans IDE 7.4and 8.0" title="Content on this page applies to the NetBeans IDE 7.4 and 8.0">

 <table class="b-none vatop" cellpadding="0" cellspacing="0">
    <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#requirements" title="Requirements">Requirements</a></td>
    </tr>
     <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#modules" title="Setting Up Your Environment for the Tutorial">
           Setting Up Your Environment for the Tutorial</a></td>
    </tr>
    <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#javaproject" title="Setting Up the Java Application
 Project">Setting Up the Java Application Project</a></td>
    </tr>
    <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#c-library" title="Setting Up a New C/C++ Dynamic Library Project">
           Setting Up a New C/C++ Dynamic Library Project</a>
 </td>
    </tr>
     <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#running" title="Building and Running the
 Application">Building and Running the Application
       </a></td>
       </tr>
        <tr>
       <td class="hyphen">-&nbsp;</td>
       <td><a href="#next" title="Next Steps">Next Steps
       </a></td>
       </tr>
 </table>

 <h2><A NAME="requirements"></a>Requirements</h2>
 <p><b>To follow this tutorial, you need the following software and resources.</b> </p>

 <table>
 <tbody>
 <tr>
 <th class="tblheader" scope="col">Software or Resource</th>
 <th class="tblheader" scope="col">Version Required</th>
 </tr>
 <tr>
 <td class="tbltd1">NetBeans IDE</td>
 <td class="tbltd1"><a
 href="https://netbeans.org/downloads/index.html">version 7.4 or 8.0 with NetBeans C/C++ plugin</a></td>
 </tr>
 <tr>
 <td class="tbltd1">Java Developer Kit (JDK)</td>
 <td class="tbltd1"><a href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">version 7 or 8</a></td>
 </tr>
 <tr>
 <td class="tbltd1">
 C and C++ compilers, <tt>make</tt>, <tt>gdb</tt></td>
    <td class="tbltd1">
    <a HREF="../../../community/releases/80/cpp-setup-instructions.html">
        Configuring the NetBeans IDE for C/C++/Fortran</a></td>
 </tr>
 </table>
 <p>See the <a href="../../../community/releases/80/install.html">NetBeans IDE
       8.0 Installation
    Instructions</a> and <a
       HREF="../../../community/releases/80/cpp-setup-instructions.html">
       Configuring the NetBeans IDE for C/C++/Fortran</a> for
    information on downloading and installing the required software.
 </p>

 <h2><a name="modules"></a>Setting Up Your Environment for the Tutorial</h2>
 <p>You need both Java modules and C/C++
 modules for this tutorial.  If you already have downloaded the NetBeans IDE C/C++ bundle,
 you can download the additional Java modules separately.</p>
 <p>To determine if you have the Java and C/C++ modules, select File &gt; New Project.
 The project categories should include both Java and C/C++.
 <p><b>To download Java and C/C++ modules that may be missing:</b></p>
 <ol><li>In the NetBeans IDE, select Tools &gt; Plugins.</li>
 <li>In the Available Plugins tab, select the checkbox for Java or C/C++, depending
 on which is missing from your IDE.  If you already have the plugins, they
 will be listed in the Installed tab.
 </li>
 <li>Click Install.</li>
 <li>Click Next in the NetBeans IDE Installer dialog box, accept the license terms checkbox,
 and click Install.</li>
 <li>Click Finish when the installation is complete.</li></ol>

 <h2><a name="javaproject"></a>Setting Up the Java Application Project</h2>
 <p>
 This program requires a Java project and a C project. In this section,
 you will create and configure the Java project for the
 JNI application you will be developing. You will create a new Java application
 project, initialize its main class, and add a native method to this class.
 </p>
 <ol>
 <li>Choose File &gt; New Project.  Select the Java category and Java Application
 project type. Click Next.<br>
 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-project-java.png" alt="Screenshot
 of the New Project Wizard" class="margin-around"></li>
 <li>In the Project Name field, type <tt>JNIDemoJava</tt>.</li>
 <li>You can change the Project Location to any directory on your computer, but here
 we use the default NetBeansProjects in the user directory.
 </li>
 <li>Leave the Create Main Class checkbox selected and change the Main class name to
 <tt>jnidemojava.Main</tt>.<br>

 <br>
 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-java-app.png" alt="Screenshot
 of the Name and Location page of the New Java Application Wizard" class="margin-around">
 </li>
 <li>Click Finish. <br> <br>
 <p>
 The IDE creates the <tt>NetBeansProjects/JNIDemoJava</tt> project folder.
 </p>
 </li>
 </ol>

 <h3>Editing the Main Class Source</h3>
 <ol>
 <li>To open the Main class source in the editor, right-click the <tt>Main.java</tt> class
 node and choose Open.</li>
 <li>Replace the line <tt>//TODO code application logic here</tt> in the <tt>main</tt> method with the following:
 <pre class="examplecode">new Main().nativePrint();</pre>
 </li>
 <li>Notice the indicator in the left margin showing an error and lightbulb. Click on the indicator,
 and you are prompted with a shortcut to create the method <tt>nativePrint</tt>.  </li>
 <li>Click on this shortcut and the IDE inserts the following code:
 <pre class="examplecode">private void nativePrint() {
       throw new UnsupportedOperationException("Not supported yet");
    }</pre>

 </li>
 <li>Delete the line
     <pre class="examplecode">throw new UnsupportedOperationException("Not supported yet");</pre>
  </li>
 <li>Modify the  <tt>nativePrint()</tt> method by
 inserting the <tt>native</tt> keyword into the method signature so that
 it now looks as follows:
 <pre class="examplecode">private native void nativePrint();</pre>
 <p>
 The <tt>native</tt> keyword indicates that the method has an implementation located in
 an external native library. However, at runtime the library location is not clear.
 </p>

 <p>The new main method should look as follows:</p>
 <pre class="examplecode">public static void main(String[] args) {
        new Main().nativePrint();
    }

    private native void nativePrint();
 }</pre>

 </li>

 <li>Right-click the project name and select Clean and Build. The project should build
 successfully.
 </li>
 </ol>
 <h3><a name="header"></a>Creating the Native Library Header File</h3>
 In this section we use <tt>javah</tt>, a Java tool that creates a C header from a Java class.
 <ol>
 <li>In a terminal window, navigate to the <tt>NetBeansProjects</tt>
 directory.
 </li>
 <li>Type the following:
 <pre class="examplecode">
 javah -o JNIDemoJava.h -classpath JNIDemoJava/build/classes jnidemojava.Main
 </pre>
 <p>
 A <tt>JNIDemoJava.h</tt> C header file is generated in the NetBeansProjects directory.
 This file is required to provide a correct function declaration for the native implementation of the
 <tt>nativePrint()</tt> method. You will need it later when you create the C part of this application.</p>
 </li>
 <li>Switch back to the NetBeans IDE window.
 </li>
 </ol>
 <p><b>Summary</b>
 <p>In this exercise you created a new Java application project,
 specified its location, and defined the package and name of the main class
 of the project. You also added a new method to the main class and marked it
 as a method having a native implementation. As a final step, you created a C
 header file, which is required later for the native library compilation.</p>

 <h2><a name="c-library"></a>Setting Up a New C/C++ Dynamic Library Project</h2>
 <p>This section shows you how to create the native part
 of the application. You will create the C++ Dynamic Library project and
 configure it to be able to build JNI code.
 </p>
 <p>After you have set up the project, you will create the implementation for
 the native method you declared earlier in the Java part of the application.

 <ol>
 <li>
 Choose File &gt; New Project. Under Categories, select C/C++. Under
 Projects, select C/C++ Dynamic Library. Click Next.
 <br>
 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-project-c.png"
 alt="Screenshot of the Choose Project page of the New Project wizard" class="margin-around">
 </li>
 <li>In the Project Name field, type <tt>JNIDemoCdl</tt>.
 </li>
 <li>In the Project Location field, use the same location that you used for
 the Java application project, <tt>NetBeansProjects</tt>. The
 location should be shown as the default value.
 </li>
 <li>Accept the defaults for all other fields and click Finish.

 <p>The IDE creates the <tt>NetBeansProjects/JNIDemoCdl</tt> project
 folder.
 </p>
 </li>
 </ol>
 <h3>Setting Project Properties</h3>
 <ol>
 <li>Right-click the JNIDemoCdl project node and choose Properties.</li>
 <li>In the Properties dialog box, select the C Compiler node under the Build properties.</li>
 <li>Click the Include Directories and Headers ... button and click Add in the Include Directories and Headers dialog box.
 <li>Browse into your JDK directory, and select the <tt>include</tt> subdirectory. </li>
 <li>Select the Store path as Absolute option, then click Select to add this directory to the project's
 Include Directories.</li>
 <li>Add the JDK's <tt>include/linux</tt> directory in the same way, then click OK.
 <br>
 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-include-directories.png" alt="Screenshot of the Project Properties dialog
 box and the Debug-Include Directories dialog box" class="margin-around">

 <p>These settings are required to enable references to the Java <tt>jni.h</tt> library
 from your C code.
 </p>
 </li>
 <li>
 Find the Compilation Line area of the C Compiler options. Click in the text field of the Additional Options
 property and type <tt>-shared -m32</tt>.

 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-project-properties-cmd-options.png"
 alt="Screenshot of the Debug-Additional Optionstext field being edited"  class="margin-around">

 <p>
 The <tt>-shared</tt> option tells the compiler to generate a dynamic library.<br>
     The
 <tt>-m32</tt> option tells the compiler to create a 32-bit binary. By default on 64-bit
 systems the compiled binaries are 64-bit, which causes a lot of problems with
 32-bit JDKs.
 </p>
 </li>
 <li>
 Click the Linker category in the left panel.</li>
 <li>Click the Output text field, and replace the string
  <pre class="examplecode">${CND_DISTDIR}/${CND_CONF}/${CND_PLATFORM}/libJNIDemoCdl.so</pre>

  with the string
  <pre class="examplecode">dist/libJNIDemoCdl.so</pre>
  to simplify the path of the resulting shared object file.
  This will make the file easer to reference from Java.<br>

 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-project-properties-linker.png"
 alt="Screenshot of the Project Properties dialog box with Linker properties" class="margin-around">


 </li>
 <li>Click OK. The defined settings are saved.
 </li>
 </ol>

 <h3>Adding a Header File</h3>
 <ol>
 <li>Go to a terminal window and move the <tt>JNIDemoJava.h</tt> header file that
 you generated previously from your <tt>NetBeansProjects</tt> directory to the
 C/C++ Library project directory, <tt>NetBeansProjects/JNIDemoCdl</tt>.
 </li>
 <li>
 <p>In the Projects window, right-click the Header Files node
 of the <tt>JNIDemoCdl</tt> project and choose Add Existing Item. Navigate to
 the  <tt>NetBeansProjects/JNIDemoCdl</tt> directory and select the <tt>JNIDemoJava.h</tt> file, then click
 Select.
 </p>
 <p>The <tt>JNIDemoJava.h</tt> file appears under Header Files.
 </p>

 <img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-source-files-include-file.png" alt="Screenshor of
 the Projects window" class="margin-around b-all">
 </li>
 </ol>
 <h3>Implementing a Method</h3>

 <ol>
 <li>Right-click the Source Files node of the <tt>JNIDemoCdl</tt> project and choose New &gt; C Source File. Type
 <tt>JNIDemo</tt> in the File Name field, and click Finish. The editor opens
 the <tt>JNIDemo.c</tt> file.
 </li>
 <li>Edit the <tt>JNIDemo.c</tt> file by typing the following code:
 <pre class="examplecode">
 #include &lt;jni.h&gt;
 #include &lt;stdio.h&gt;
 #include "JNIDemoJava.h"

 JNIEXPORT void JNICALL Java_jnidemojava_Main_nativePrint
         (JNIEnv *env, jobject obj)
 {

     printf("\nHello World from C\n");

 }
 </pre>
 </li>
 <li>Save the <tt>JNIDemo.c</tt> file.</li>
 <li>
 Right-click the <tt>JNIDemoCdl</tt> project node and choose Build. The
 Output window displays <tt>BUILD SUCCESSFUL (total time 171ms)</tt> or similar.
 </li>
 </ol>
 <p><b>Summary</b></p>

 <p>In this exercise you created a new C/C++ Dynamic Library, specified its
 location, and configured it to be able to build a JNI implementation of your
 Java method. You added the generated header file for the native method you
 declared in the Java application, and implemented it.
 </p>

 <h2><a name="running"></a>Building and Running the Application</h2>
 <p>
 In this exercise, you will perform some final alterations to the Java part of
 the application. These changes are required to ensure the Java part properly
 loads the native library you compiled in the previous exercise. After that you
 will compile and run the resulting application.
 </p>
 <div class="indent">
 <h3>Configuring the Java Project</h3>
 <ol>
 <li>Open the <tt>Main.java</tt> file in the editor.
 <li>Add the following initialization code for the C++ dynamic library after the <tt>public class Main</tt> line, using the path to the output file
 that you shortened
 in the previous exercise:
 <pre class="examplecode">
 static {
         System.load("<i>full-path-to-NetBeansProjects-dir</i>/JNIDemoCdl/dist/libJNIDemoCdl.so");
        }
 </pre>
 Replace <i>full-path-to-NetBeansProjects-dir</i> with the path to your NetBeansProjects directory,
 which should be something similar to
 <tt>/home/<i>username</i>/NetBeansProjects</tt>

 </li>
 <li>Save the <tt>Main.java</tt> file.</li>

 </ol>
 <h3>Running the JNIDemoJava Application</h3>
 <ol><li>Select the JNIDemoJava application in the Projects window.</li>
 <li>Press F6 or click the Run button in the toolbar to run the application.
 The program should execute correctly and the Output window should display output similar to the following:
 <br>
 <img src="../../../images_www/articles/72/cnd/beginning-jni-linux/jni-build-success.png"
 alt="Screenshot of the Output window" class="margin-around">
 </li>
 </ol>
 <h3>Summary</h3>
 <p>In this exercise you made some final configuration steps and ran the
 application to verify that the implementation of the native method comes from
 the native C library.
 </p>
 </div>
 <h2><a name="next"></a>Next Steps</h2>
 <p>If you want to check your work against a working example, you can
 <a href="https://netbeans.org/projects/samples/downloads/download/Samples%252FCPlusPlus%252FJNIDemo.zip" target="_blank">
     download a zip file containing the source code</a> from netbeans.org.
 </p>


 <p>
 You can use the following documents to get more information:
 <ul>
 <li><a href="quickstart.html">
 C/C++ Projects Quick Start Tutorial</a>
 <li><a href="http://docs.oracle.com/javase/7/docs/technotes/guides/jni/" target="_blank">JNI Specification</a></li>
 <li><a href="http://en.wikipedia.org/wiki/Java_Native_Interface" target="_blank">Java Native Interface</a>

 </ul>
   <DIV CLASS="feedback-box">
    <A
       HREF="https://netbeans.org/about/contact_form.html?to=7&amp;subject=Feedback:%20Beginning%20JNI%20with%20NetBeans%20IDE%20and%20C/C++%20Plugin%20on%20Linux">Send Feedback on This Tutorial</a>
 </DIV>
 </body>
 </html>
	<html>
	<head>
	<title>Beginning JNI with NetBeans IDE and C/C++ Plugin on Linux</title>
	<meta name="DESCRIPTION" content="A tutorial describing how to compile
	and run JNI powered Java applications using NetBeans IDE or Oracle Solaris Studio IDE.">
	<meta name="author" content="Susan Morgan"><!--Optional tag-->
	<link rel="stylesheet" type="text/css" href="../../../netbeans.css">
	<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" >
	</head>
	<body>
	<a name="top"></a>

	<h1>Beginning JNI with NetBeans IDE and C/C++ Plugin on Linux</h1>
	<!-- START INTRO ---------------------------------------------------------------------------------------* -->
	<div class="articledate" style="margin-left: 0px;font-style:italic;">
	<!-- <p><em>Contributed by <i>Susan Morgan</i> <br> -->
	<em>March 2014</em> [Revision number: V8.0-1]</div>

	<p>This tutorial takes you through the creation of a simple application that
	uses Java<sup><small>TM</small></sup> Native Interface (JNI) code written in the C
	programming language.
	<p class="notes">The tutorial is specific to Linux.</p>
	<!-- END INTRO -->

	<h3>Contents</h3>
	<img src="../../../images_www/articles/74/netbeans-stamp-80-74.png" class="stamp"
	alt="Content on this page applies to NetBeans IDE 7.4and 8.0" title="Content on this page applies to the NetBeans IDE 7.4 and 8.0">

	<table class="b-none vatop" cellpadding="0" cellspacing="0">
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#requirements" title="Requirements">Requirements</a></td>
	</tr>
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#modules" title="Setting Up Your Environment for the Tutorial">
	Setting Up Your Environment for the Tutorial</a></td>
	</tr>
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#javaproject" title="Setting Up the Java Application
	Project">Setting Up the Java Application Project</a></td>
	</tr>
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#c-library" title="Setting Up a New C/C++ Dynamic Library Project">
	Setting Up a New C/C++ Dynamic Library Project</a>
	</td>
	</tr>
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#running" title="Building and Running the
	Application">Building and Running the Application
	</a></td>
	</tr>
	<tr>
	<td class="hyphen">- </td>
	<td><a href="#next" title="Next Steps">Next Steps
	</a></td>
	</tr>
	</table>

	<h2><A NAME="requirements"></a>Requirements</h2>
	<p><b>To follow this tutorial, you need the following software and resources.</b> </p>

	<table>
	<tbody>
	<tr>
	<th class="tblheader" scope="col">Software or Resource</th>
	<th class="tblheader" scope="col">Version Required</th>
	</tr>
	<tr>
	<td class="tbltd1">NetBeans IDE</td>
	<td class="tbltd1"><a
	href="https://netbeans.org/downloads/index.html">version 7.4 or 8.0 with NetBeans C/C++ plugin</a></td>
	</tr>
	<tr>
	<td class="tbltd1">Java Developer Kit (JDK)</td>
	<td class="tbltd1"><a href="http://www.oracle.com/technetwork/java/javase/downloads/index.html">version 7 or 8</a></td>
	</tr>
	<tr>
	<td class="tbltd1">
	C and C++ compilers, <tt>make</tt>, <tt>gdb</tt></td>
	<td class="tbltd1">
	<a HREF="../../../community/releases/80/cpp-setup-instructions.html">
	Configuring the NetBeans IDE for C/C++/Fortran</a></td>
	</tr>
	</table>
	<p>See the <a href="../../../community/releases/80/install.html">NetBeans IDE
	8.0 Installation
	Instructions</a> and <a
	HREF="../../../community/releases/80/cpp-setup-instructions.html">
	Configuring the NetBeans IDE for C/C++/Fortran</a> for
	information on downloading and installing the required software.
	</p>

	<h2><a name="modules"></a>Setting Up Your Environment for the Tutorial</h2>
	<p>You need both Java modules and C/C++
	modules for this tutorial. If you already have downloaded the NetBeans IDE C/C++ bundle,
	you can download the additional Java modules separately.</p>
	<p>To determine if you have the Java and C/C++ modules, select File > New Project.
	The project categories should include both Java and C/C++.
	<p><b>To download Java and C/C++ modules that may be missing:</b></p>
	<ol><li>In the NetBeans IDE, select Tools > Plugins.</li>
	<li>In the Available Plugins tab, select the checkbox for Java or C/C++, depending
	on which is missing from your IDE. If you already have the plugins, they
	will be listed in the Installed tab.
	</li>
	<li>Click Install.</li>
	<li>Click Next in the NetBeans IDE Installer dialog box, accept the license terms checkbox,
	and click Install.</li>
	<li>Click Finish when the installation is complete.</li></ol>

	<h2><a name="javaproject"></a>Setting Up the Java Application Project</h2>
	<p>
	This program requires a Java project and a C project. In this section,
	you will create and configure the Java project for the
	JNI application you will be developing. You will create a new Java application
	project, initialize its main class, and add a native method to this class.
	</p>
	<ol>
	<li>Choose File > New Project. Select the Java category and Java Application
	project type. Click Next.<br>
	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-project-java.png" alt="Screenshot
	of the New Project Wizard" class="margin-around"></li>
	<li>In the Project Name field, type <tt>JNIDemoJava</tt>.</li>
	<li>You can change the Project Location to any directory on your computer, but here
	we use the default NetBeansProjects in the user directory.
	</li>
	<li>Leave the Create Main Class checkbox selected and change the Main class name to
	<tt>jnidemojava.Main</tt>.<br>

	<br>
	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-java-app.png" alt="Screenshot
	of the Name and Location page of the New Java Application Wizard" class="margin-around">
	</li>
	<li>Click Finish. <br> <br>
	<p>
	The IDE creates the <tt>NetBeansProjects/JNIDemoJava</tt> project folder.
	</p>
	</li>
	</ol>

	<h3>Editing the Main Class Source</h3>
	<ol>
	<li>To open the Main class source in the editor, right-click the <tt>Main.java</tt> class
	node and choose Open.</li>
	<li>Replace the line <tt>//TODO code application logic here</tt> in the <tt>main</tt> method with the following:
	<pre class="examplecode">new Main().nativePrint();</pre>
	</li>
	<li>Notice the indicator in the left margin showing an error and lightbulb. Click on the indicator,
	and you are prompted with a shortcut to create the method <tt>nativePrint</tt>. </li>
	<li>Click on this shortcut and the IDE inserts the following code:
	<pre class="examplecode">private void nativePrint() {
	throw new UnsupportedOperationException("Not supported yet");
	}</pre>

	</li>
	<li>Delete the line
	<pre class="examplecode">throw new UnsupportedOperationException("Not supported yet");</pre>
	</li>
	<li>Modify the <tt>nativePrint()</tt> method by
	inserting the <tt>native</tt> keyword into the method signature so that
	it now looks as follows:
	<pre class="examplecode">private native void nativePrint();</pre>
	<p>
	The <tt>native</tt> keyword indicates that the method has an implementation located in
	an external native library. However, at runtime the library location is not clear.
	</p>

	<p>The new main method should look as follows:</p>
	<pre class="examplecode">public static void main(String[] args) {
	new Main().nativePrint();
	}

	private native void nativePrint();
	}</pre>

	</li>

	<li>Right-click the project name and select Clean and Build. The project should build
	successfully.
	</li>
	</ol>
	<h3><a name="header"></a>Creating the Native Library Header File</h3>
	In this section we use <tt>javah</tt>, a Java tool that creates a C header from a Java class.
	<ol>
	<li>In a terminal window, navigate to the <tt>NetBeansProjects</tt>
	directory.
	</li>
	<li>Type the following:
	<pre class="examplecode">
	javah -o JNIDemoJava.h -classpath JNIDemoJava/build/classes jnidemojava.Main
	</pre>
	<p>
	A <tt>JNIDemoJava.h</tt> C header file is generated in the NetBeansProjects directory.
	This file is required to provide a correct function declaration for the native implementation of the
	<tt>nativePrint()</tt> method. You will need it later when you create the C part of this application.</p>
	</li>
	<li>Switch back to the NetBeans IDE window.
	</li>
	</ol>
	<p><b>Summary</b>
	<p>In this exercise you created a new Java application project,
	specified its location, and defined the package and name of the main class
	of the project. You also added a new method to the main class and marked it
	as a method having a native implementation. As a final step, you created a C
	header file, which is required later for the native library compilation.</p>

	<h2><a name="c-library"></a>Setting Up a New C/C++ Dynamic Library Project</h2>
	<p>This section shows you how to create the native part
	of the application. You will create the C++ Dynamic Library project and
	configure it to be able to build JNI code.
	</p>
	<p>After you have set up the project, you will create the implementation for
	the native method you declared earlier in the Java part of the application.

	<ol>
	<li>
	Choose File > New Project. Under Categories, select C/C++. Under
	Projects, select C/C++ Dynamic Library. Click Next.
	<br>
	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-new-project-c.png"
	alt="Screenshot of the Choose Project page of the New Project wizard" class="margin-around">
	</li>
	<li>In the Project Name field, type <tt>JNIDemoCdl</tt>.
	</li>
	<li>In the Project Location field, use the same location that you used for
	the Java application project, <tt>NetBeansProjects</tt>. The
	location should be shown as the default value.
	</li>
	<li>Accept the defaults for all other fields and click Finish.

	<p>The IDE creates the <tt>NetBeansProjects/JNIDemoCdl</tt> project
	folder.
	</p>
	</li>
	</ol>
	<h3>Setting Project Properties</h3>
	<ol>
	<li>Right-click the JNIDemoCdl project node and choose Properties.</li>
	<li>In the Properties dialog box, select the C Compiler node under the Build properties.</li>
	<li>Click the Include Directories and Headers ... button and click Add in the Include Directories and Headers dialog box.
	<li>Browse into your JDK directory, and select the <tt>include</tt> subdirectory. </li>
	<li>Select the Store path as Absolute option, then click Select to add this directory to the project's
	Include Directories.</li>
	<li>Add the JDK's <tt>include/linux</tt> directory in the same way, then click OK.
	<br>
	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-include-directories.png" alt="Screenshot of the Project Properties dialog
	box and the Debug-Include Directories dialog box" class="margin-around">

	<p>These settings are required to enable references to the Java <tt>jni.h</tt> library
	from your C code.
	</p>
	</li>
	<li>
	Find the Compilation Line area of the C Compiler options. Click in the text field of the Additional Options
	property and type <tt>-shared -m32</tt>.

	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-project-properties-cmd-options.png"
	alt="Screenshot of the Debug-Additional Optionstext field being edited" class="margin-around">

	<p>
	The <tt>-shared</tt> option tells the compiler to generate a dynamic library.<br>
	The
	<tt>-m32</tt> option tells the compiler to create a 32-bit binary. By default on 64-bit
	systems the compiled binaries are 64-bit, which causes a lot of problems with
	32-bit JDKs.
	</p>
	</li>
	<li>
	Click the Linker category in the left panel.</li>
	<li>Click the Output text field, and replace the string
	<pre class="examplecode">${CND_DISTDIR}/${CND_CONF}/${CND_PLATFORM}/libJNIDemoCdl.so</pre>

	with the string
	<pre class="examplecode">dist/libJNIDemoCdl.so</pre>
	to simplify the path of the resulting shared object file.
	This will make the file easer to reference from Java.<br>

	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-project-properties-linker.png"
	alt="Screenshot of the Project Properties dialog box with Linker properties" class="margin-around">



	</li>
	<li>Click OK. The defined settings are saved.
	</li>
	</ol>

	<h3>Adding a Header File</h3>
	<ol>
	<li>Go to a terminal window and move the <tt>JNIDemoJava.h</tt> header file that
	you generated previously from your <tt>NetBeansProjects</tt> directory to the
	C/C++ Library project directory, <tt>NetBeansProjects/JNIDemoCdl</tt>.
	</li>
	<li>
	<p>In the Projects window, right-click the Header Files node
	of the <tt>JNIDemoCdl</tt> project and choose Add Existing Item. Navigate to
	the <tt>NetBeansProjects/JNIDemoCdl</tt> directory and select the <tt>JNIDemoJava.h</tt> file, then click
	Select.
	</p>
	<p>The <tt>JNIDemoJava.h</tt> file appears under Header Files.
	</p>

	<img src="../../../images_www/articles/74/cnd/beginning-jni-linux/jni-source-files-include-file.png" alt="Screenshor of
	the Projects window" class="margin-around b-all">
	</li>
	</ol>
	<h3>Implementing a Method</h3>

	<ol>
	<li>Right-click the Source Files node of the <tt>JNIDemoCdl</tt> project and choose New > C Source File. Type
	<tt>JNIDemo</tt> in the File Name field, and click Finish. The editor opens
	the <tt>JNIDemo.c</tt> file.
	</li>
	<li>Edit the <tt>JNIDemo.c</tt> file by typing the following code:
	<pre class="examplecode">
	#include <jni.h>
	#include <stdio.h>
	#include "JNIDemoJava.h"

	JNIEXPORT void JNICALL Java_jnidemojava_Main_nativePrint
	(JNIEnv *env, jobject obj)
	{

	printf("\nHello World from C\n");

	}
	</pre>
	</li>
	<li>Save the <tt>JNIDemo.c</tt> file.</li>
	<li>
	Right-click the <tt>JNIDemoCdl</tt> project node and choose Build. The
	Output window displays <tt>BUILD SUCCESSFUL (total time 171ms)</tt> or similar.
	</li>
	</ol>
	<p><b>Summary</b></p>

	<p>In this exercise you created a new C/C++ Dynamic Library, specified its
	location, and configured it to be able to build a JNI implementation of your
	Java method. You added the generated header file for the native method you
	declared in the Java application, and implemented it.
	</p>

	<h2><a name="running"></a>Building and Running the Application</h2>
	<p>
	In this exercise, you will perform some final alterations to the Java part of
	the application. These changes are required to ensure the Java part properly
	loads the native library you compiled in the previous exercise. After that you
	will compile and run the resulting application.
	</p>
	<div class="indent">
	<h3>Configuring the Java Project</h3>
	<ol>
	<li>Open the <tt>Main.java</tt> file in the editor.
	<li>Add the following initialization code for the C++ dynamic library after the <tt>public class Main</tt> line, using the path to the output file
	that you shortened
	in the previous exercise:
	<pre class="examplecode">
	static {
	System.load("<i>full-path-to-NetBeansProjects-dir</i>/JNIDemoCdl/dist/libJNIDemoCdl.so");
	}
	</pre>
	Replace <i>full-path-to-NetBeansProjects-dir</i> with the path to your NetBeansProjects directory,
	which should be something similar to
	<tt>/home/<i>username</i>/NetBeansProjects</tt>

	</li>
	<li>Save the <tt>Main.java</tt> file.</li>

	</ol>
	<h3>Running the JNIDemoJava Application</h3>
	<ol><li>Select the JNIDemoJava application in the Projects window.</li>
	<li>Press F6 or click the Run button in the toolbar to run the application.
	The program should execute correctly and the Output window should display output similar to the following:
	<br>
	<img src="../../../images_www/articles/72/cnd/beginning-jni-linux/jni-build-success.png"
	alt="Screenshot of the Output window" class="margin-around">
	</li>
	</ol>
	<h3>Summary</h3>
	<p>In this exercise you made some final configuration steps and ran the
	application to verify that the implementation of the native method comes from
	the native C library.
	</p>
	</div>
	<h2><a name="next"></a>Next Steps</h2>
	<p>If you want to check your work against a working example, you can
	<a href="https://netbeans.org/projects/samples/downloads/download/Samples%252FCPlusPlus%252FJNIDemo.zip" target="_blank">
	download a zip file containing the source code</a> from netbeans.org.
	</p>


	<p>
	You can use the following documents to get more information:
	<ul>
	<li><a href="quickstart.html">
	C/C++ Projects Quick Start Tutorial</a>
	<li><a href="http://docs.oracle.com/javase/7/docs/technotes/guides/jni/" target="_blank">JNI Specification</a></li>
	<li><a href="http://en.wikipedia.org/wiki/Java_Native_Interface" target="_blank">Java Native Interface</a>

	</ul>
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