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<h1 class="topictitle1">Download and install Java packages</h1>
<div><p>To download, install, and use Java™ packages more effectively on an iSeries™ server,
see the following topics.</p>
<p><strong>Packages with graphical user interfaces</strong></p>
<p>Java programs
used with graphical user interface (GUI) require the use of a presentation
device with graphical display capabilities. For example, you can use a personal
computer, technical workstation, or network computer. You can use Native Abstract
Windowing Toolkit (NAWT) to provide your Java applications and servlets with the
full capability of the Java 2 Software Development Kit (J2SDK),
Standard Edition Abstract Windowing Toolkit (AWT) graphics functions. For
more information, see <a href="nawt.htm">Native Abstract Windowing Toolkit
(NAWT)</a>.</p>
<p><strong>Case sensitivity and integrated file system</strong></p>
<p>Integrated file system provides file systems, which are both case-sensitive
and those that are not with regard to file names. QOpenSys is an example of
a case-sensitive file system within the integrated file system. Root, '/',
is an example of a case-insensitive file system. For more information, see
the <a href="../ifs/rzaaxkickoff.htm" target="_blank">Integrated
file system</a> topic.</p>
<p> Even though a JAR or class may be located in a case-insensitive file system, Java is
still a case-sensitive language. While <samp class="codeph">wrklnk '/home/Hello.class'</samp> and <samp class="codeph">wrklnk
'/home/hello.class'</samp> produce the same results, <samp class="codeph">JAVA CLASS(Hello)</samp> and <samp class="codeph">JAVA
CLASS(hello)</samp> are calling different classes. </p>
<p><strong>ZIP file handling and JAR file handling</strong></p>
<p>ZIP files and JAR files contain a set of Java classes. When you use the <a href="../cl/crtjvapgm.htm" target="_blank">Create Java Program
(CRTJVAPGM)</a> command on one of these files, the classes are verified,
converted to an internal machine form, and if specified, transformed to iSeries machine
code. You can treat ZIP files and JAR files like any other individual class
file. When an internal machine form is associated with one of these files,
it remains associated with the file. The internal machine form is used on
future runs in place of the class file to improve performance. If you are
unsure whether a current Java program is associated with your class
file or JAR file, use the <a href="../cl/dspjvapgm.htm" target="_blank"> Display Java Program (DSPJVAPGM)</a> command
to display information about your Java program on your iSeries server.</p>
<p>In previous releases of the IBM<sup>®</sup> Developer Kit for Java, you
had to recreate a Java program if you changed the JAR file or ZIP file
in any way, because the attached Java program would become unusable. This
is no longer true. In many cases, if you change a JAR file or ZIP file, the Java program
is still valid and you do not have to recreate it. If partial changes are
made, such as when a single class file is updated within a JAR file, you only
need to recreate the affected class files that are within the JAR file.</p>
<p>Java programs
remain attached to the JAR file after most typical changes to the JAR file.
For example, these Java programs remain attached to the JAR
file when:</p>
<ul><li>Changing or recreating a JAR file by using the <a href="javatool.htm">ajar
tool</a>.</li>
<li>Changing or recreating a JAR file by using the <a href="javatool.htm">jar
tool</a>.</li>
<li>Replacing a JAR file by using the 0S/400 COPY command or the Qshell <samp class="codeph">cp</samp> utility.</li>
</ul>
<p>If you access a JAR file in the integrated file system through iSeries Access
for Windows<sup>®</sup> or
from a mapped drive on a personal computer (PC), these Java programs
remain attached to the JAR file when:</p>
<ul><li>Dragging and dropping another JAR file onto the existing integrated file
system JAR file.</li>
<li>Changing or recreating the integrated file system JAR file by using the <a href="javatool.htm">jar tool</a>.</li>
<li>Replacing the integrated file system JAR file by using the PC copy command.</li>
</ul>
<p>When a JAR file is changed or replaced, the Java program that is attached to it is no
longer current.</p>
<p>There is one exception in which Java programs do not remain attached to
the JAR file. The attached Java programs are destroyed if you use file
transfer protocol (FTP) to replace the JAR file. For example, this occurs
if you use the FTP <samp class="codeph">put</samp> command to replace the JAR file.</p>
<p>See <a href="runtperf.htm">Java runtime performance</a> for more
detailed information about the performance characteristics of JAR files.</p>
<p><strong>Java extensions
framework</strong></p>
<p>In J2SDK, extensions are packages of Java classes that you can use to extend
the functionality of the core platform. An extension or application is packaged
in one or more JAR files. The extension mechanism allows the Java virtual
machine to use the extension classes in the same way that the virtual machine
uses the system classes. The extension mechanism also provides a way for you
to retrieve extensions from specified URLs when they are not already installed
in the J2SDK or Java 2 Runtime Environment, Standard Edition.</p>
<p>See <a href="instextn.htm">Install extensions for the IBM Developer
Kit for Java</a> for information on installing extensions.</p>
</div>
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<div class="familylinks">
<div class="parentlink"><strong>Parent topic:</strong> <a href="install.htm" title="Installing IBM Developer Kit for Java allows you to create and run Java programs on your iSeries server.">Install IBM Developer Kit for Java</a></div>
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