public class TEST extends JFrame{
    ... blah, blah.....
	
    private void launch(){
	setBounds(200, 200, 100, 100);
	setDefaultCloseOperation(EXIT_ON_CLOSE);
	
	JPanel greenPanel = new JPanel();
	greenPanel.setSize(70, 70); //<---- xNot resize the greenPanel
	greenPanel.setBackground(Color.green);
	
	JPanel yellowPanel = new JPanel();
	yellowPanel.setSize(50, 50); //<-- xNot resize yellowPanel in greenPanel
	yellowPanel.setBackground(Color.yellow);
	greenPanel.add(yellowPanel);
	
	JPanel bluePanel = new JPanel();
	bluePanel.setBackground(Color.blue);
	bluePanel.add(greenPanel);
	
	add(bluePanel);
	
	setVisible(true);
    }
}

So, I have a yellow JPanel inside a green JPanel inside a blue JPanel.. For some reason, none of the JPanels resize, only the JFrame...

Here's a picture:
http://img225.imageshack.us/img225/5460/jpanelbashsn7.png

Any ideas?

First of all, I want to say thanks! I had hard time doing JPanel over JPanel and in such colourful box.

change your setSize into setPreferredSize(new Dimension(int length, int width))