The Java(TM) 2 Runtime Environment is intended for software developers and vendors to redistribute with their applications.

The Java 2 Runtime Environment contains the Java virtual machine, runtime class libraries, and Java application launcher that are necessary to run programs written in the Java programming language.

It is not a development environment and does not contain development tools such as compilers or debuggers.
For development tools, see the Java 2 SDK, Standard Edition. Download this Sun Java JRE 1.5.0.09