Code

public class TestFrame extends JFrame {
	private Diagram diag;
	private DiagramView view;

	public TestFrame() {

		diag = new Diagram();
		diag.setBounds(new Rectangle2D.Float(0, 0, 300, 300));

		view = new DiagramView(diag);

		this.addComponentListener(new ComponentAdapter() {
		    public void componentResized(ComponentEvent e) {
		    	Rectangle pixelSize = view.docToDevice(diag.getBounds());
		    	if (pixelSize.width < TestFrame.this.getWidth() ||
		    		pixelSize.height < TestFrame.this.getHeight())
		    	{
		    		pixelSize.width = Math.max(pixelSize.width, TestFrame.this.getWidth());
		    		pixelSize.height = Math.max(pixelSize.height, TestFrame.this.getHeight());
		    		diag.setBounds(view.deviceToDoc(pixelSize));
		    	}
		    }
		});
...