The development of J2SE 5.0 was led by Sun and progressed following the Java Community Process (JCP) to include input from a variety of constituents. Some highlights of J2SE 5.0:

New language updates: Metadata, Generics, Enumerated types, Autoboxing of primitive types, New JVM Monitoring and Management API, Improved out-of-box performance
New (but compatible) default Java look and feel.
There are two principal products in the J2SE platform family: J2SE Runtime Environment (JRE) and J2SE Development Kit (JDK). The JRE provides the Java APIs, Java virtual machine, and other components necessary to run applets and applications written in the Java programming language. It is also the foundation for the technologies in the Java 2 Platform, Enterprise Edition (J2EE) for enterprise software development and deployment. The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications.

The JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applets and applications.
The J2SE application programming interface (API) defines the prescribed manner by which an applet or application can make requests to and use the functionality available in the compiled J2SE class libraries. The J2SE class libraries are also part of the J2SE platform.

The J2SE API consists of technologies we have organized into two groups: Core Java and Desktop Java.

Core Java provides essential functionality for writing powerful enterprise-worthy programs in key areas such as database access, security, remote method invocation (RMI), and communications, to name a few.

Desktop Java provides a full range of features to help build desktop applications that provide a rich user experience. Desktop Java consists of deployment products such as Java Plug-in, component modeling APIs such as JavaBeans, graphical user interface (GUI) APIs such as the Java Foundation Classes (JFC) and Swing, and multimedia APIs such as Java3D.
To learn more about Java Desktop, visit the Desktop Java community collaboration site and java.com consumer site. For information on how to use the J2SE APIs, refer to the API (Javadocs) and technical documentation.

The Java Virtual Machine is responsible for the hardware- and operating system-independence of the J2SE platform, the small size of compiled code (bytecodes), and platform security.

The J2SE platform works with an array of tools, including Integrated Development Environments (IDEs), performance and testing tools, and performance monitoring tools.