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<?xml version="1.0" encoding="UTF-8"?>
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<!-- $Header: /var/cvsroot/gentoo/xml/htdocs/doc/en/java.xml,v 1.14 2005/03/06 12:08:19 swift Exp $ -->
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<!DOCTYPE guide SYSTEM "/dtd/guide.dtd">
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<guide link="/doc/en/java.xml">
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<title>Gentoo Java Guide</title>
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<author title="Author and Editor">
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<mail link="karltk@gentoo.org">Karl Trygve Kalleberg</mail>
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</author>
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<author title="Editor">
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<mail link="swift@gentoo.org">Sven Vermeulen</mail>
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</author>
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<author title="Editor">
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<mail link="vanquirius@gentoo.org">Marcelo Góes</mail>
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</author>
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<abstract>
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This guide will introduce users and developers to Java and explain how to use
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Java with Gentoo Linux.
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</abstract>
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<license/>
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<version>0.1.6</version>
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<date>2005-03-06</date>
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<chapter>
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<title>What is Java?</title>
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<section>
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<title>Overview</title>
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<body>
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<p>
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Java is a programming language developed by engineers of Sun Microsystems.
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The language is object-oriented and designed to run on multiple platforms
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without the need of recompiling code for each platform. Although Java can
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be compiled as a native program, much of Java's popularity can be attributed
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to its portability, along with other features such as garbage collection.
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The ability to compile once and run in various platforms is achieved through
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the use of just-in-time compilers (JIT), which compile Java bytecodes into
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native code when a given program is run.
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</p>
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<p>
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In order to run Java bytecodes, one needs to have a JRE (Java Runtime Environment)
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installed. A JRE provides core libraries, a platform dependent Java Virtual Machine,
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plug-ins for browsers, among other things. A JDK (Java Development Kit) adds
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programming tools, such as a bytecode compiler and a debugger.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Installing a JRE/JDK</title>
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<section>
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<title>The choices</title>
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<body>
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<p>
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Gentoo provides numerous JREs and JDKs. Among the current alternatives, we have:
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</p>
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<ul>
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<li>blackdown-jre and blackdown-jdk, the Blackdown Java Kit</li>
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<li>sun-jre-bin and sun-jdk, Sun's Java Kit </li>
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<li>ibm-jre-bin and ibm-jdk-bin, the IBM Java Kit</li>
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<li>compaq-jre and compaq-jdk, the Compaq Java Kit for Alpha/Linux/GNU</li>
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<li>jrockit-jdk-bin, BEA WebLogic's J2SE Development Kit</li>
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</ul>
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<p>
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The default is the Blackdown JRE/JDK
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pair, as it is freely ("free as in beer") available without any registration
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fuss.
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</p>
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<p>
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Both the Sun JRE/JDK and the IBM JRE/JDK are generally faster, but getting them
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is a bit more work, as you are required to read and accept their license before
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downloading (IBM additionally requires you to register).
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</p>
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<p>
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Our ebuilds for the Sun and IBM JRE/JDKs will notify you of where to go to
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download them.
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</p>
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</body>
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</section>
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<section>
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<title>Installing the Sun/IBM JRE/JDKs</title>
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<body>
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<p>
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If you run <c>emerge =sun-jdk-1.4.2.06</c> or <c>=ibm-jdk-bin-1.4.2</c>, you will
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be notified that you are required to download the actual tarballs yourself. This
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has to do with license restrictions for the Sun JRE/JDK (online click-wrap
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license) and registration issues with the IBM JRE/JDK.
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</p>
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<note>
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ibm-jdk-bin is currently masked, you may have to unmask it to use it.
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</note>
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<p>
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You should download the indicated file(s) into
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<path>/usr/portage/distfiles</path>. Once that is done, you can rerun the emerge
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command, then the JRE/JDK will be installed properly into <path>/opt</path>.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Configuring your JRE/JDK</title>
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<section>
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<title>Overview</title>
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<body>
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<p>
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Gentoo has the ability to have multiple JDKs and JREs installed without them
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conflicting.
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</p>
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<p>
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Using the <c>java-config</c> tool, you can set the system-wide default if you
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have root access. Users can also use <c>java-config</c> to set up their own
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personal default, that is different from the system-wide default.
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</p>
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</body>
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</section>
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<section>
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<title>Setting a default JRE/JDK</title>
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<body>
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<p>
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Running the command <c>java-config --list-available-vms</c> will give you a list
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of all available JREs and JDKs on your system. Here is an example of output:
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</p>
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<pre caption="Listing available VMs">
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# <i>java-config --list-available-vms</i>
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[blackdown-jdk-1.3.1] Blackdown JDK 1.3.1 (/etc/env.d/java/20blackdown-jdk-1.3.1)
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[blackdown-jre-1.3.1] Blackdown JRE 1.3.1 (/etc/env.d/java/20blackdown-jre-1.3.1)
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[ibm-jdk-1.3.0] IBM JDK 1.3.0 (/etc/env.d/java/20ibm-jdk-1.3.0)
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[ibm-jdk-1.3.1] IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
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[ibm-jre-1.3.1] IBM JRE 1.3.1 (/etc/env.d/java/20ibm-jre-1.3.1)
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[sun-jdk-1.4.0] Sun JDK 1.4.0 (/etc/env.d/java/20sun-jdk-1.4.0)
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</pre>
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<p>
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The name in the brackets <path>"[]"</path> is the handle or ID for that
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particular VM. You use pass that ID to <c>java-config --set-system-vm</c>. Here is
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an example of how to set the system VM.
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</p>
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<pre caption="Setting the System VM">
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# <i>java-config --set-system-vm=ibm-jdk-1.3.1</i>
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Now using IBM JDK 1.3.1 (/etc/env.d/java/20ibm-jdk-1.3.1)
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</pre>
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<note>
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You will have to be root to run --set-system-vm.
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</note>
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<p>
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Once you have issued <c>java-config --set-system-vm</c> with a particular VM ID,
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you will need to regenerate your /etc/profile.env. You can do it like this:
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</p>
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<pre caption="Regenerating /etc/profile.env" >
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# <i>env-update</i>
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</pre>
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<p>
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After this, you will either want to relogin, or resource
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<path>/etc/profile</path> into your environment.
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</p>
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<p>
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As a regular user, you can use <c>java-config --set-user-vm</c>, which will
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create <path>~/.gentoo/java-env</path> with all required env vars. You would
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normally source this from your shell's startup script
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(generally <path>~/.bashrc</path>).
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</p>
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</body>
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</section>
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<section>
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<title>Setting a default CLASSPATH</title>
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<body>
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<p>
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<c>java-config</c> can also be used to set a system-wide default CLASSPATH, and
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of course a user-specific default CLASSPATH.
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</p>
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<p>
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First you want to list available java libraries that might be interesting to put
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in your CLASSPATH. Here is an example of output:
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</p>
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<pre caption="Listing classes">
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# <i>java-config --list-available-packages</i>
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[bsh] BeanShell is a small, free, embeddable, Java
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source interpreter with object scripting language
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features. (/usr/share/bsh/package.env)
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[oro] A set of text-processing Java classes that
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provide Perl5 compatible regular expressions, AWK-like
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regular expressions, glob expressions, and utility
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classes for performing substitutions, splits, filtering
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filenames, etc. (/usr/share/oro/package.env)
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[bcel] The Byte Code Engineering Library: analyze, create,
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manipulate Java class files (/usr/share/bcel/package.env)
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[jsch] JSch is a pure Java implementation of SSH2.
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(/usr/share/jsch/package.env)
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...
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</pre>
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<p>
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Again, the name in brackets <path>"[]"</path> are the IDs that you have to pass
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to <c>java-config --set-system-classpath</c>. Here is an example:
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</p>
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<pre caption="Setting classpaths">
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# <i>java-config --set-system-classpath=log4j,java-gtk,java-gnome</i>
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</pre>
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<note>
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The current directory (.) will not be part of the system classpath, as that
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should be added in root's login profile.
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</note>
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<p>
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Again, you will want to run <c>env-update</c> to update your system's
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environment, and you might also want to relogin or resource the
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<path>/etc/profile</path>.
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</p>
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<p>
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For users, <c>java-config --set-user-classpath</c> will create
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<path>~/.gentoo/java-env-classpath</path>, which is automatically included
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by <path>~/.gentoo/java-env</path>.
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</p>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>USE flags for use with Java</title>
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<section>
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<title>Setting USE flags</title>
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<body>
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<p>
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For more information regarding USE flags, refer to the
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<uri link="/doc/en/handbook/handbook-x86.xml?part=2&chap=2">USE flags</uri>
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chapter from the Gentoo Handbook.
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</p>
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</body>
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</section>
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<section>
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<title>The flags</title>
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<body>
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<ul>
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<li>The <b>java</b> flag adds support for Java in a variety of programs.</li>
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<li>The <b>mozilla</b> flag adds support for Mozilla-like browsers (including Firefox)
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if you are using blackdown's Java kit. You will need this for viewing Java applets
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in your Mozilla-like browser.</li>
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</ul>
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</body>
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</section>
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</chapter>
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<chapter>
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<title>Additional resources</title>
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<section>
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<title>Off-line resources</title>
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<body>
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<ul>
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<li>java-config man page</li>
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<li><c>java-config --help</c></li>
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<li>The <path>/usr/bin/java-config</path> script itself</li>
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</ul>
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</body>
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</section>
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<section>
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<title>Online resources</title>
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<body>
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<ul>
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<li>The <uri link="http://news.gmane.org/gmane.linux.gentoo.devel"
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>gentoo-dev</uri>, <uri link="http://news.gmane.org/gmane.linux.gentoo.user"
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>gentoo-user </uri> mailing list archives</li>
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<li>#gentoo and #gentoo-java on irc.freenode.net</li>
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<li><uri link="http://en.wikipedia.org/wiki/Java_programming_language">Wikipedia's entry for Java</uri></li>
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</ul>
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</body>
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</section>
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</chapter>
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</guide>
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