JDK File Structure

This document gives an overview of the JDK directories and the files they contain.

Development Files and Directories

This section describes the files and directories that are required to develop apps for the Java platform. (The directories that are not required include demos, Java 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:

                 jdk1.2
        ___________|____________________
       |           |                    |
      bin         lib                  jre
       |           |          __________|___________
   java.exe    tools.jar     |                      |        
   javac.exe   dt.jar       bin                    lib                
   javap.exe            _____|____          ________|________          
   javah.exe           |          |        |        |        |         
   javadoc.exe     java.exe    classic   rt.jar    ext    security
                   java.dll       |      i18n.jar   |                  
                   awt.dll     jvm.dll            iiimp.jar

Assuming the JDK software is installed at c:\jdk1.2, here are the crucial directories and why they are important:

c:\jdk1.2

The root directory of the JDK software installation. Contains copyright, license, and README files. Also includes:

src.jar -- the archive of source files for all the classes that make up the Java platform's core API.

c:\jdk1.2\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:\jdk1.2\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:\jdk1.2\jre

The root directory of the Java runtime environment used by the JDK development tools. The runtime environment is an implementation of the Java 1.2 platform. It is exactly the same as the deployable JRE, minus the documentation.

c:\jdk1.2\jre\bin

Executable files and DLLs for tools and libraries used by the Java platform. The executable files are identical to files in /jdk1.2/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:\jdk1.2\jre\bin\classic

Contains the Windows DLL files used by the classic VM. The classic VM is the language-interpreter version of the Java Virtual Machine. When newer virtual machines are available, their DLLs will be installed in a new subdirectory of jre/bin.

c:\jdk1.2\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).
i18n.jar -- the character-conversion classes and other files associated with internationalization and localization.

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

c:\jdk1.2\jre\lib\ext

Default installation directory for Extensions to the Java platform. This is where the JavaHelp jar file goes when it is installed, for example. Includes:

iiimp.jar -- the classes that implement the Internet-Intranet Input Method Protocol, used by apps that accept input from devices using an international character set.

c:\jdk1.2\jre\lib\security

Contains files used for security management. These include the security policy (java.policy) and security properties (java.security) files.

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:

                   jdk1.2
      __________ _____|_____ _____________
     |          |           |             |
   src.jar    demo       include     include-old
             ___|___
            |       |  
          applets  jfc
                    |
                  Java2D

The additional directories shown above are:

c:\jdk1.2\demo

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

c:\jdk1.2\demo\applets

Applets that can be used on a Web page.

c:\jdk1.2\demo\jfc

Examples that use the new JFC\Swing components.

c:\jdk1.2\demo\jfc\Java2D

Examples that use the new Java 2D graphics.

c:\jdk1.2\include

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

c:\jdk1.2\include-old

Header files that support native-code programming using older interfaces. These header files are provided only for backward-compatibility. These interfaces are deprecated, unsupported and not available on all Java virtual machines.