JDK

The Java Developement Kit, or JDK, is a set of tools,resources, utilities, documentation, and sample code for developing Java programs. 

GETTING THE LATEST VERSION

Before you get started learning about the Java Developer's Kit,you must make sure that you have the latest version. 
so download the latest version JDK 7.
The Java Developer's Kit contains a variety of tools and Java development information. There is a list of the main components of the JDK:
The Runtime Interpreter
The Compiler
The Applet Viewer
The Debugger
The Class File Disassembler
The Header and Stub File Generator
The Documentation Generator
Applet Demos
API Source Code