# 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 location (URL) of the Javadoc
- 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

You can switch the default JRE for the workbench. The default JRE is the JRE to which the pre-defined classpath variables JRE_LIB, JRE_SRC and JRE_SRCROOT are bound.

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
Editing a JRE definition
Overriding the default system libraries for a JRE definition
Viewing and editing a project's build path

Installed JREs preference page