This document gives an overview of the Java 2 SDK, Standard Edition,
directories and the files they contain. This page may also be used as
a reference for the file structure of the Java 2 Runtime Environment.
To see the file structure of the Runtime Environment, just look at the
description of the contents of the SDK's jre directory on this
page.
The file structure of the Java 2 Runtime Environment is identical to that
of the SDK's jre directory.
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, 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:
Assuming the SDK software is installed at c:\jdk1.3, here are some of the most important directories:
c:\jdk1.3
The root directory of the SDK software installation. Contains copyright, license, and README files. Also contains src.jar, the archive
of source code for the Java 2 platform.
c:\jdk1.3\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 SDK
Tools.
c:\jdk1.3\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 SDK. 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:\jdk1.3\jre
The root directory of the Java runtime environment used by the SDK
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:\jdk1.3\jre\bin
Executable files and DLLs for tools and libraries used by the Java platform. The executable files are identical
to files in /jdk1.3/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 SDK software. This directory does not need to
be in the PATH environment variable.
c:\jdk1.3\jre\bin\classic
Contains the DLL files used by the Java 2 Classic
Virtual Machine. These files are present only in the Java 2 SDK.
They are not included with the Java 2 Runtime Environment.
c:\jdk1.3\jre\bin\hotspot
Contains the DLL files used by the Java HotSpotTM Client Virtual
Machine, which is implemented with Java HotSpot technology.
c:\jdk1.3\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:\jdk1.3\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.
c:\jdk1.3\jre\lib\security
Contains files used for security management. These include the security policy (java.policy) and
security properties (java.security) files.
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 the local file system by the applet class loader,
providing the same protections as if they had been downloaded over the
net.
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:
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.