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<title>Classpath</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Classpath</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">For the software, see <a href="GNU_Classpath" title="GNU Classpath">GNU Classpath</a>.</div>

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<p><b>Classpath</b> is a parameter in the <a href="Java_virtual_machine" title="Java virtual machine">Java Virtual Machine</a> or the <a href="Java_compiler" title="Java compiler">Java compiler</a> that specifies the location of user-defined <a href="Class_(computer_science)" class="mw-redirect" title="Class (computer science)">classes</a> and <a href="Java_package" title="Java package">packages</a>. The parameter may be set either on the <a href="Command_line_interface" class="mw-redirect" title="Command line interface">command-line</a>, or through an <a href="Environment_variable" title="Environment variable">environment variable</a>.

</p>

<div class="mw-heading mw-heading2"><h2 id="Overview_and_architecture">Overview and architecture</h2></div>

<div role="note" class="hatnote navigation-not-searchable">See also: <a href="Java_class_loader" title="Java class loader">Java class loader</a></div>

<p>Similar to the classic <a href="Library_(computing)#Dynamic_loading" title="Library (computing)">dynamic loading</a> behavior, when executing <a href="Java_(programming_language)" title="Java (programming language)">Java</a> programs, the <a href="Java_virtual_machine" title="Java virtual machine">Java Virtual Machine</a> finds and loads classes lazily (it loads the <a href="Java_bytecode" title="Java bytecode">bytecode</a> of a class only when the class is first used). The classpath tells Java where to look in the filesystem for files defining these classes.

</p><p>The virtual machine searches for and loads classes in this order:

</p>

<ol><li>bootstrap classes: the classes that are fundamental to the <a href="Java_Platform" class="mw-redirect" title="Java Platform">Java Platform</a> (comprising the public classes of the <a href="Java_Class_Library" title="Java Class Library">Java Class Library</a>, and the private classes that are necessary for this library to be functional).</li>

<li>extension classes: <a href="Java_package" title="Java package">packages</a> that are in the <i>extension</i> directory of the <a href="Java_Runtime_Environment" class="mw-redirect" title="Java Runtime Environment">Java Runtime Environment</a> or <a href="JDK" class="mw-redirect" title="JDK">JDK</a>, <code>jre/lib/ext/</code></li>

<li>user-defined packages and libraries</li></ol>

<p>By default only the packages of the <a href="JDK" class="mw-redirect" title="JDK">JDK</a> <a href="Java_Platform%2C_Standard_Edition" title="Java Platform, Standard Edition">standard API</a> and extension packages are accessible without needing to set where to find them. The path for all user-defined <a href="Java_package" title="Java package">packages</a> and libraries must be set in the command-line (or in the <a href="Manifest_file" title="Manifest file">Manifest</a> associated with the <a href="JAR_(file_format)" title="JAR (file format)">Jar file</a> containing the classes).

</p>

<div class="mw-heading mw-heading2"><h2 id="Setting_the_path_to_execute_Java_programs">Setting the path to execute Java programs</h2></div>

<div class="mw-heading mw-heading3"><h3 id="Supplying_as_application_argument">Supplying as application argument</h3></div>

<p>Suppose we have a package called <i>org.mypackage</i> containing the classes:

</p>

<ul><li><i>HelloWorld</i> (main class)</li>

<li><i>SupportClass</i></li>

<li><i>UtilClass</i></li></ul>

<p>and the files defining this package are stored physically under the directory <i>D:\myprogram</i> (on <a href="Microsoft_Windows" title="Microsoft Windows">Windows</a>) or <i>/home/user/myprogram</i> (on <a href="Linux" title="Linux">Linux</a>).

</p><p>The file structure looks like this:

</p>

<th><a href="Microsoft_Windows" title="Microsoft Windows">Microsoft Windows</a>

</th>

<th><a href="Linux" title="Linux">Linux</a>

</th></tr>

<tr>

<td><pre>D:\myprogram\

---> org\

---> mypackage\

---> HelloWorld.class

---> SupportClass.class

---> UtilClass.class

</pre>

</td>

<td><pre>/home/user/myprogram/

---> org/

---> mypackage/

---> HelloWorld.class

---> SupportClass.class

---> UtilClass.class

</pre>

</td></tr>

</tbody></table>

<p>When we invoke Java, we specify the name of the application to run: org.mypackage.HelloWorld. However we must also tell Java where to look for the files and directories defining our package. So to launch the program, we use the following command:

</p>

<th><a href="Microsoft_Windows" title="Microsoft Windows">Microsoft Windows</a>

</th>

<th><a href="Linux" title="Linux">Linux</a>

</th></tr>

<tr>

<td><pre> java -classpath D:\myprogram org.mypackage.HelloWorld

</pre>

</td>

<td><pre> java -cp /home/user/myprogram org.mypackage.HelloWorld

</pre>

</td></tr>

</tbody></table>

<p>where:

</p>

<ul><li><code>java</code> is the <a href="Java_runtime" class="mw-redirect" title="Java runtime">Java runtime</a> launcher, a type of SDK Tool (A command-line tool, such as <a href="Javac" title="Javac">javac</a>, <a href="Javadoc" title="Javadoc">javadoc</a>, or <a href="APT_(software)" title="APT (software)">apt</a>)</li>

<li><i>-classpath D:\myprogram</i> sets the path to the packages used in the program (on Linux, <i>-cp /home/user/myprogram</i>) and</li>

<li><i>org.mypackage.HelloWorld</i> is the name of the main class</li></ul>

<div class="mw-heading mw-heading3"><h3 id="Setting_the_path_through_an_environment_variable">Setting the path through an environment variable</h3></div>

<p>The <a href="Environment_variable" title="Environment variable">environment variable</a> named <code>CLASSPATH</code> may be alternatively used to set the classpath. For the above example, we could also use on Windows:

</p>

<div class="mw-highlight mw-highlight-lang-doscon mw-content-ltr" dir="ltr"><pre><span class="gp">D:\myprogram></span><span class="k">set</span> <span class="nv">CLASSPATH</span><span class="p">=</span>D:\myprogram

<span class="gp">D:\myprogram></span>java org.mypackage.HelloWorld

</pre></div>

<p>The rule is that <code>-classpath</code> option, when used to start the java application, overrides the <code>CLASSPATH</code> environment variable. If none are specified, the <a href="Working_directory" title="Working directory">current working directory</a> is used as classpath. This means that when our working directory is <code>D:\myprogram\</code> (on Linux, <code>/home/user/myprogram/</code>), we would not need to specify the classpath explicitly. When overriding however, it is advised to include the current folder <code>"."</code> into the classpath in the case when loading classes from current folder is desired.

</p><p>The same applies not only to java launcher but also to <a href="Javac" title="Javac">javac</a>, the java compiler.

</p>

<div class="mw-heading mw-heading3"><h3 id="Setting_the_path_of_a_Jar_file">Setting the path of a Jar file</h3></div>

<p>If a program uses a supporting library enclosed in a <a href="JAR_(file_format)" title="JAR (file format)">Jar file</a> called <i>supportLib.jar</i>, physically located in the directory <i>D:\myprogram\lib\</i> and the corresponding physical file structure is:

</p>

<pre>D:\myprogram\

---> lib\

---> supportLib.jar

---> org\

---> mypackage\

---> HelloWorld.class

---> SupportClass.class

---> UtilClass.class

</pre>

<p>the following <a href="Command-line_interface#Command-line_option" title="Command-line interface">command-line option</a> is needed:

</p>

<pre>java -classpath D:\myprogram;D:\myprogram\lib\supportLib.jar org.mypackage.HelloWorld

</pre>

<p>or alternatively:

</p>

<span class="gp">D:\myprogram></span>java org.mypackage.HelloWorld

</pre></div>

<div class="mw-heading mw-heading3"><h3 id="Adding_all_JAR_files_in_a_directory">Adding all JAR files in a directory</h3></div>

<p>In <a href="Java_6" class="mw-redirect" title="Java 6">Java 6</a> and higher, one can add all jar-files in a specific directory to the classpath using wildcard notation.

</p><p>Windows example:

</p>

<div class="mw-highlight mw-highlight-lang-doscon mw-content-ltr" dir="ltr"><pre><span class="gp">D:\myprogram></span>java -classpath <span class="s2">".;c:\mylib\*"</span> MyApp

</pre></div>

<p>Linux example:

</p>

<div class="mw-highlight mw-highlight-lang-console mw-content-ltr" dir="ltr"><pre><span class="gp">$ </span>java<span class="w"> </span>-classpath<span class="w"> </span><span class="s1">'.:/mylib/*'</span><span class="w"> </span>MyApp

</pre></div>

<p>This works for both <code>-classpath</code> options and environment classpaths.

</p>

<div class="mw-heading mw-heading3"><h3 id="Setting_the_path_in_a_manifest_file">Setting the path in a manifest file</h3></div>

<p>If a program has been enclosed in a <a href="JAR_(file_format)" title="JAR (file format)">Jar file</a> called <i>helloWorld.jar</i>, located directly in the directory <i>D:\myprogram</i>, the directory structure is as follows:

</p>

<pre>D:\myprogram\

---> helloWorld.jar

---> lib\

---> supportLib.jar

</pre>

<p>The <a href="Manifest_file" title="Manifest file">manifest file</a> defined in <i>helloWorld.jar</i> has this definition:

</p>

<div class="mw-highlight mw-highlight-lang-properties mw-content-ltr" dir="ltr"><pre><span class="na">Main-Class</span><span class="o">:</span><span class="w"> </span><span class="s">org.mypackage.HelloWorld</span>

<span class="na">Class-Path</span><span class="o">:</span><span class="w"> </span><span class="s">lib/supportLib.jar</span>

</pre></div>

<p>The <a href="Manifest_file" title="Manifest file">manifest file</a> should end with either a new line or carriage return.

</p><p>The program is launched with the following command:

</p>

<pre>java -jar D:\myprogram\helloWorld.jar [app arguments]

</pre>

<p>This automatically starts <i>org.mypackage.HelloWorld</i> specified in class <i>Main-Class</i> with the arguments. The user cannot replace this class name using the invocation <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">java -jar</code>. <i>Class-Path</i> describes the location of <i>supportLib.jar</i> relative to the location of the library <i>helloWorld.jar</i>. Neither absolute file path, which is permitted in <code class="mw-highlight mw-highlight-lang-text mw-content-ltr" style="" dir="ltr">-classpath</code> parameter on the command line, nor jar-internal paths are supported. This means that if the main class file is contained in a jar, <i>org/mypackage/HelloWorld.class</i> must be a valid path on the root within the jar.

</p><p>Multiple classpath entries are separated with spaces:

</p>

<div class="mw-highlight mw-highlight-lang-properties mw-content-ltr" dir="ltr"><pre><span class="na">Class-Path</span><span class="o">:</span><span class="w"> </span><span class="s">lib/supportLib.jar lib/supportLib2.jar</span>

</pre></div>

<div class="mw-heading mw-heading2"><h2 id="OS_specific_notes">OS specific notes</h2></div>

<p>Being closely associated with the file system, the <a href="Command-line_argument" class="mw-redirect" title="Command-line argument">command-line</a> Classpath syntax depends on the operating system.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup> For example:

</p>

<ul><li>on all <a href="Unix" title="Unix">Unix-like</a> operating systems (such as <a href="Linux" title="Linux">Linux</a> and <a href="Mac_OS_X" class="mw-redirect" title="Mac OS X">Mac OS X</a>), the directory structure has a Unix syntax, with separate file paths separated by a <a href="Colon_(punctuation)" title="Colon (punctuation)">colon</a> (":").</li>

<li>on <a href="Microsoft_Windows" title="Microsoft Windows">Windows</a>, the directory structure has a Windows syntax, and each file path must be separated by a <a href="Semicolon" title="Semicolon">semicolon</a> (";").</li></ul>

<p>This does not apply when the Classpath is defined in <a href="Manifest_file" title="Manifest file">manifest files</a>, where each file path must be separated by a space (" "), regardless of the operating system.

</p>

<ul><li><a href="Java_class_loader" title="Java class loader">Java class loader</a></li>

<li><a href="Java_Platform_Module_System" title="Java Platform Module System">Java Platform Module System</a></li>

<li><a href="Rpath" title="Rpath">rpath</a> – Hard-coded search path</li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://www.antwerkz.com/blog/the-classpath">"The Classpath"</a>. 6 August 2013<span class="reference-accessdate">. Retrieved <span class="nowrap">2016-06-26</span></span>.</cite></span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://docs.oracle.com/javase/6/docs/technotes/tools/findingclasses.html">Note explaining how Java classes are found, on Oracle website</a></li>

<li><a rel="nofollow" class="external text" href="http://docs.oracle.com/javase/1.5.0/docs/tooldocs/windows/classpath.html">Specification of how to set the Classpath on Oracle site</a></li></ul></div><div><div class="zim-footer">

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