Java Platform, Standard Edition Tools Reference
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3 JDK and JRE File Structure

This chapter introduces the JDK directories and the files they contain. The file structure of the JRE is identical to the structure of the jre directory in the JDK.

This chapter covers the following topics:

Development Files and Directories

This section describes the most important files and directories required to develop applications for the Java platform. Some of the directories that are not required include Java source code and C header files. See Additional Files and Directories.

jdk-1.8
     bin
          java*
          javac*
          javap*
          javah*
          javadoc*
     lib
          tools.jar
          dt.jar
     jre
          bin
               java*
          lib
               applet
               ext
                    jfxrt.jar
                    localdata.jar
               fonts
               security
               sparc
                    server
                    client
               rt.jar
               charsets.jar

Assuming the JDK software is installed at /jdk-1.8, here are some of the most important directories:

/jdk-1.8

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 platform.

/jdk-1.8/bin

Executables for all the development tools contained in the JDK. The PATH environment variable should contain an entry for this directory.

/jdk-1.8/lib

Files used by the development tools. Includes 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 (IDEs) how to display the Java components and how to let the developer customize them for an application.

/jdk-1.8/jre

Root directory of the Java Runtime Environment (JRE) used by the JDK development tools. The runtime environment is an implementation of the Java platform. This is the directory referred to by the java.home system property.

/jdk-1.8/jre/bin

Executable files for tools and libraries used by the Java platform. The executable files are identical to files in /jdk-1.8/bin. The java launcher tool serves as an application launcher. This directory does not need to be in the PATH environment variable.

/jdk-1.8/jre/lib

Code libraries, property settings, and resource files used by the JRE. For example rt.jar contains the bootstrap classes, which are the run time classes that comprise the Java platform core API, and charsets.jar contains the character-conversion classes. Aside from the ext subdirectory, there are several additional resource subdirectories not described here.

/jdk-1.8/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. This directory includes the jfxrt.jar file, which contains the JavaFX runtime libraries and the localedata.jar file, which contains the locale data for the java.text and java.util packages. See The Extension Mechanism.

/jdk-1.8/jre/lib/security

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

/jdk-1.8/jre/lib/applet

JAR files that contain 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 preloaded from the local file system by the applet class loader and provides the same protections as though they had been downloaded over the Internet.

/jdk-1.8/jre/lib/fonts

Font files used by the platform.

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