Assuming the JDK software is installed at c:\jdk1.7.0, here are some of the most important directories:
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.
- rt.jar -- the bootstrap classes (the RunTime classes that comprise the Java platform's core API).
- localedata.jar -- locale data for java.text and java.util.
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.