The default JRE is used for compiling and launching Java programs in all projects
unless you specifically override the default JRE on a project's build path or
on a launch configuration.
Check the box on the line for the JRE that you want to assign as the default JRE in your workbench.
If the JRE you want to assign as the default does not appear in the list, you must add it.
Click OK.
Note: Changing the default JRE may cause a build to occur if
you have auto build enabled (Project > Build Automatically
or in the General >
Workspace preference page).
Java > Installed JREs preference page.