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<title>GNU Octave: How to make Java classes available?</title>
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<a name="How-to-make-Java-classes-available_003f"></a>
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<p>
Next: <a href="How-to-create-an-instance-of-a-Java-class_003f.html#How-to-create-an-instance-of-a-Java-class_003f" accesskey="n" rel="next">How to create an instance of a Java class?</a>, Previous: <a href="How-to-distinguish-between-Octave-and-Matlab_003f.html#How-to-distinguish-between-Octave-and-Matlab_003f" accesskey="p" rel="prev">How to distinguish between Octave and Matlab?</a>, Up: <a href="FAQ-_002d-Frequently-asked-Questions.html#FAQ-_002d-Frequently-asked-Questions" accesskey="u" rel="up">FAQ - Frequently asked Questions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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<hr>
<a name="How-to-make-Java-classes-available-to-Octave_003f"></a>
<h4 class="subsection">37.3.2 How to make Java classes available to Octave?</h4>
<a name="index-classpath_002c-setting"></a>
<a name="index-classpath_002c-difference-between-static-and-dynamic"></a>
<a name="index-static-classpath-1"></a>
<a name="index-dynamic-classpath-1"></a>
<a name="index-javaclasspath_002etxt"></a>
<a name="index-classpath_002etxt"></a>
<a name="index-classes_002c-making-available-to-Octave"></a>
<p>Java finds classes by searching a <var>classpath</var>. This is a list of Java
archive files and/or directories containing class files. In Octave
the <var>classpath</var> is composed of two parts:
</p>
<ul>
<li> the <var>static classpath</var> is initialized once at startup of the JVM, and
</li><li> the <var>dynamic classpath</var> which can be modified at runtime.
</li></ul>
<p>Octave searches the <var>static classpath</var> first, then the <var>dynamic
classpath</var>. Classes appearing in the <var>static</var> as well as in the
<var>dynamic classpath</var> will therefore be found in the <var>static classpath</var>
and loaded from this location. Classes which will be used frequently or must
be available to all users should be added to the <var>static classpath</var>. The
<var>static classpath</var> is populated once from the contents of a plain text file
named <samp>javaclasspath.txt</samp> (or <samp>classpath.txt</samp> historically) when the
Java Virtual Machine starts. This file contains one line for each individual
classpath to be added to the <var>static classpath</var>. These lines can identify
single class files, directories containing class files, or Java archives with
complete class file hierarchies. Comment lines starting with a ‘<samp>#</samp>’ or a
‘<samp>%</samp>’ character are ignored.
</p>
<p>The search rules for the file <samp>javaclasspath.txt</samp>
(or <samp>classpath.txt</samp>) are:
</p>
<ul>
<li> First, Octave tries to locate it in the current directory (where Octave
was started from). If such a file is found, it is read and defines the initial
<var>static classpath</var>. Thus, it is possible to define a static classpath on a
’per Octave invocation’ basis.
</li><li> Next, Octave searches in the user’s home directory. If a file
<samp>javaclasspath.txt</samp> exists here, its contents are appended to the static
classpath (if any). Thus, it is possible to build an initial static classpath
on a ’per user’ basis.
</li><li> Finally, Octave looks for a next occurrence of file
<samp>javaclasspath.txt</samp> in the m-files directory where Octave Java functions
live. This is where <samp>javaclasspath.m</samp> resides, usually something like
<samp><code><span class="nolinebreak">OCTAVE_HOME</span></code><!-- /@w -->/share/octave/<code><span class="nolinebreak">OCTAVE_VERSION</span></code><!-- /@w -->/m/java/</samp>. You can
find this directory by executing the command
<div class="example">
<pre class="example">which javaclasspath
</pre></div>
<p>If this file exists here, its contents are also appended to the static
classpath. Note that the archives and class directories defined in this last
step will affect all users.
</p></li></ul>
<p>Classes which are used only by a specific script should be placed in the
<var>dynamic classpath</var>. This portion of the classpath can be modified at
runtime using the <code>javaaddpath</code> and <code>javarmpath</code> functions.
</p>
<p>Example:
</p>
<div class="example">
<pre class="example">octave> base_path = "C:/Octave/java_files";
octave> % add two JARchives to the dynamic classpath
octave> javaaddpath ([base_path, "/someclasses.jar"]);
octave> javaaddpath ([base_path, "/moreclasses.jar"]);
octave> % check the dynamic classpath
octave> p = javaclasspath;
octave> disp (p{1});
C:/Octave/java_files/someclasses.jar
octave> disp (p{2});
C:/Octave/java_files/moreclasses.jar
octave> % remove the first element from the classpath
octave> javarmpath ([base_path, "/someclasses.jar"]);
octave> p = javaclasspath;
octave> disp (p{1});
C:/Octave/java_files/moreclasses.jar
octave> % provoke an error
octave> disp (p{2});
error: A(I): Index exceeds matrix dimension.
</pre></div>
<p>Another way to add files to the <var>dynamic classpath</var> exclusively for your
user account is to use the file <samp>.octaverc</samp> which is stored in your home
directory. All Octave commands in this file are executed each time you start a
new instance of Octave. The following example adds the directory <samp>octave</samp>
to Octave’s search path and the archive <samp>myclasses.jar</samp> in this directory
to the Java search path.
</p>
<div class="example">
<pre class="example">% contents of .octaverc:
addpath ("~/octave");
javaaddpath ("~/octave/myclasses.jar");
</pre></div>
<hr>
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Next: <a href="How-to-create-an-instance-of-a-Java-class_003f.html#How-to-create-an-instance-of-a-Java-class_003f" accesskey="n" rel="next">How to create an instance of a Java class?</a>, Previous: <a href="How-to-distinguish-between-Octave-and-Matlab_003f.html#How-to-distinguish-between-Octave-and-Matlab_003f" accesskey="p" rel="prev">How to distinguish between Octave and Matlab?</a>, Up: <a href="FAQ-_002d-Frequently-asked-Questions.html#FAQ-_002d-Frequently-asked-Questions" accesskey="u" rel="up">FAQ - Frequently asked Questions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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