# Working with JREs

You can install as many different Java Runtime Environments (JREs) as you like. JREs are used to run and debug java programs. Your JREs are managed on the Installed JREs preference page.

A JRE definition consists of:

- The type of the JRE (e.g. Standard VM or Standard 1.x.x VM)
- A name
- The location where the JRE is installed
- The system libraries containing the Java system classes (like java.lang.Object). Optionally, the system libraries can be associated with the source file containing the source for the classes in the JRE's CLASS files and a javadoc location (URL).
- Other information needed by the VM to build, run and debug applications.

You can switch the default JRE for the workbench. The default JRE is used by default when building, running, and debugging applications. Alternatively, projects may specify a specific JRE that they should be built and run with.

Java development tools (JDT)

Adding a new JRE definition
Deleting a JRE definition
Choosing a default JRE
Choosing a JRE for launching a project

Installed JREs preference page