JDK and JRE File Structure

JDK Tools

This document gives an overview of the JDK directories and the files they contain. This page may also be used as a reference for the file structure of the JRE. To see the file structure of the Runtime Environment, just look at the description of the contents of the JDK's jre directory on this page. The file structure of the JRE is identical to that of the JDK's jre directory.

Development Files and Directories

This section describes the files and directories that are required to develop apps for the Java 2 Platform. (The directories that are not required include demos, source code, and C header files. They are discussed in the following section, Additional Files and Directories.) The following chart shows the most important directories:

               jdk1.5.0
        ___________|____________________
       |           |                    |
      bin         lib                  jre
       |           |          __________|_____________________
   java.exe    tools.jar     |                                |        
   javac.exe   dt.jar       bin                              lib                
   javap.exe            _____|____ __________         ________|_______ ________ ________        
   javah.exe           |          |          |       |        |       |        |        |
   javadoc.exe     java.exe    client      server  rt.jar    ext  security  applet    fonts
                   java.dll       |          |   charsets.jar |                  
                   awt.dll     jvm.dll    jvm.dll        localedata.jar

Assuming the JDK software is installed at c:\jdk1.5.0, here are some of the most important directories:

c:\jdk1.5.0

The root directory of the JDK software installation. Contains copyright, license, and README files. Also contains src.zip, the archive of source code for the Java 2 platform.

c:\jdk1.5.0\bin

The executable files for the development tools contained in the Java Development Kit. The PATH environment variable should contain an entry for this directory. For more information on the tools, see the JDK Tools.

c:\jdk1.5.0\lib

Files used by the development tools. These include tools.jar, which contains non-core classes for support of the tools and utilities in the JDK. Also includes dt.jar, the DesignTime archive of BeanInfo files that tell interactive development environments (IDE's) how to display the Java components and how to let the developer customize them for the application.

c:\jdk1.5.0\jre

The root directory of the Java runtime environment used by the JDK development tools. The runtime environment is an implementation of the Java 2 platform. This is the directory represented by the java.home system property.

c:\jdk1.5.0\jre\bin

Executable files and DLLs for tools and libraries used by the Java platform. The executable files are identical to files in /jdk1.5.0/bin. The java launcher tool serves as an application launcher, in place of the old jre tool that shipped with 1.1 versions of the JDK software. This directory does not need to be in the PATH environment variable.

c:\jdk1.5.0\jre\bin\client

Contains the DLL files used by the Java 2 HotSpot Client Virtual Machine.

c:\jdk1.5.0\jre\bin\server

Contains the DLL files used by the Java HotSpot Server Virtual Machine.

c:\jdk1.5.0\jre\lib

Code libraries, property settings, and resource files used by the Java runtime environment. Includes:

rt.jar -- the bootstrap classes (the RunTime classes that comprise the Java platform's core API).
charsets.jar -- character conversion classes.

Aside from the ext subdirectory (described below) there are several additional resource subdirectories not described here.

c:\jdk1.5.0\jre\lib\ext

Default installation directory for Extensions to the Java platform.

localedata.jar -- locale data for java.text and java.util.

c:\jdk1.5.0\jre\lib\security

Contains files used for security management. These include the security policy (java.policy) and security properties (java.security) files.
c:\jdk1.5.0\jre\lib\applet

Jar files containing support classes for applets can be placed in the lib/applet/ directory. This reduces startup time for large applets by allowing applet classes to be pre-loaded from teh local file system by the applet class loader, providing the same protections as if they had been downloaded over the net.

c:\jdk1.5.0\jre\lib\fonts

Contains TrueType font files for use by the platform.

Additional Files and Directories

This section describes the directory structure for the demos, Java source code, and C header files. Here is the directory structure:

                        jdk1.5.0
                 ___________|__________ 
                |           |          |       
              demo      include     src.zip
             ___|___ _________ __________
            |       |         |          |
          applets  jfc       jpda      plugin

The additional directories shown above are:

c:\jdk1.5.0\src.zip

Archive containing source code for the Java 2 platform.

c:\jdk1.5.0\demo

Examples, with source code, that show you how to program for the Java platform.

c:\jdk1.5.0\demo\applets

Applets that can be used on a Web page.

c:\jdk1.5.0\demo\jfc

Examples that use Java 2D^TM and JFC\Swing functionality.

c:\jdk1.5.0\demo\jpda

Examples of using the Java Platform Debugging Architecture. Includes source code for the javadt and jdb utilities.

c:\jdk1.5.0\demo\plugin

Contains demos for use with Java Plug-in product.

c:\jdk1.5.0\include

C-language header files that support native-code programming using the Java Native Interface and the Java Virtual Machine Debugger Interface.

Java Software