# Working with JREs

You can install as many different Java Runtime Environments (JREs) as you like. 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).

You can switch the default JRE for the workbench. The default JRE is used by default when building, running, and debugging applications.

Java development tools (JDT)
Classpath variable

Adding a new JRE definition
Assigning the default JRE for the workbench
Choosing a JRE for launching a project
Deleting a JRE definition

Installed JREs preference page