JDK and JRE File Structure

Assuming the JDK software is installed at c:\jdk1.7.0, here are some of the most important directories:


Root directory of the JDK software installation. Contains copyright, license, and README files. Also contains, the archive of source code for the Java platform.


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.


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 an application.


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


Executable files and DLLs for tools and libraries used by the Java platform. The executable files are identical to files in /jdk1.7.0/bin. The java launcher tool serves as an application launcher (and replaced the old jretool that shipped with 1.1 versions of the JDK). This directory does not need to be in the PATH environment variable.


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


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


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


Default installation directory for Extensions to the Java platform.

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


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


Contains TrueType font files for use by the platform.

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