System.exit();
causes the Java VM to terminate completely.
JFrame.dispose();
causes the JFrame
window to be destroyed and cleaned up by the operating system. According to the documentation, this can cause the Java VM to terminate if there are no other Windows available, but this should really just be seen as a side effect rather than the norm.
The one you choose really depends on your situation. If you want to terminate everything in the current Java VM, you should use System.exit()
and everything will be cleaned up. If you only want to destroy the current window, with the side effect that it will close the Java VM if this is the only window, then use JFrame.dispose()
.