Sample Code(In the sample subdirectory) Samples, with source code, of programming for certain Java API's.

These include examples that use Swing and other Java Foundation Classes, and the Java Platform Debugger Architecture.

Demo Applets and Applications(In the demo/ subdirectory) Examples, with source code, of programming for the Javaplatform.

Additional Libraries(In the lib/ subdirectory) Additional class libraries and support files required by the development tools.

The JRE includes a Java Virtual Machine (JVM), class libraries, and other files that support the execution of programs written in the Java programming language.

Runtime Environment(In the jre/ subdirectory) An implementation of the Java Runtime Environment (JRE) for use by the JDK.

Development Tools(In the bin/ subdirectory) Tools and utilities that will help you develop, execute, debug, and document programs written in the JavaTM programming language.

This tool also helps manage JAR files, javadoc - the documentation generator, which automatically generates documentation from source code comments, jdb - the debugger, jps - the process status tool, which displays process information for current Java processes, javap - the class file disassembler, and other components are also included.

JDK has a collection of programming tools, including javac, jar, and the archiver, which packages related class libraries into a single JAR file. Java Development Kit contains the software and tools that you need to compile, debug, and run applets and applications written using the Java programming language. Java Development Kit is the official development kit for the Java programming language.

Java 8 101