The work for JDK 1.6 started with the name Project Mustang and released on December, 2006. This version is known as Java SE 6 instead of J2SE. This version includes lot of features in GUI execution speed etc. Following list gives.
GUI Desktop: The package java.awt is reinforced with more classes useful to integrate GUI applications with other GUI technologies.
More support for Internationalization: We know that Java is known as i18n language as it supports characters of many international languages like Telugu, Tamil, Malayalam, Thai, Latin etc. The internationalization supports the user inputs and outputs in his own mother-tongue.
Improvements in Swing: javax.swing components are lightweight. Still to integrate the swing components with the underlying OS, the designers introduced more classes. These classes also eliminate gray-area affect and allow table sorting and filtering etc.
Adding Icons: System tray capability is introduced to add icons and tooltips etc.
Compiler: New type of compilers are introduced. Now a Java program can be compiled programmatically (need not from command-prompt).
Debugger: Debugger architecture of Java platform is changed.
Memory Leaks: New options are added to JVM to run script when the heap is full. It avoids memory leaks.
Security support: The added extra security features allows integration with GSS/Kerberos security systems.
JDBC 4.0: JDBC is added with more features.
JDK 1.7 (Java SE 7) Features
The new features added with JDK 1.7 are: JDK 1.7 Features
Refer for all Java Versions.
Following links gets you JDK 1.7 version