I have a read several books on java and studying for the SCJP exam.
Everything I have read says that Java draws the controls (for example a button). Where other languages / frameworks like .Net, QT framework, SWT, and wxWidgets create instances of the native controls from the OS.
That swing will create instances of native controls rather then draw them when you use:
The default Look and Feel (LAF) for Swing is the Metal LAF.
When you use: UIManager.getSystemLookAndFeelClassName() it doesn't not mean that native controls will be used. It means that Swing will use the default LAF for the platform the application is running on. The controls will be painted by Swing to look like the controls for that platform.
Both WindowsLookAndFeel and GTKLookAndFeel are using native invocations to paint themselves. That's why they are using much more memory than "pure java" LookAndFeels, because abstraction level is doubled