For each file, you can set whether it is run with external execution (in a new Java VM) or internal execution (useful if you want to modify the IDE itself). You can also use applet execution or any other type of execution available through the installed modules.

To change the type of execution for an object, first select its icon in the Explorer. Then, on its property sheet (in the Properties window), click the Execution tab. Select the Executor property and then click on the drop-down arrow that appears and choose the execution type from the combo box.

The executors themselves can be configured in the Explorer under Project Settings | Execution Types.