import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Area;
import java.awt.geom.Rectangle2D;
 
import javax.swing.JFrame;
import javax.swing.JPanel;
 
 
public class Test extends JPanel {
 
    public static void main(String[] args) {
        JFrame f = new JFrame();
        Test t = new Test();
        f.getContentPane().setLayout(new BorderLayout());
        f.getContentPane().add(t,BorderLayout.CENTER);
        f.pack();
        f.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
        f.setVisible(true);
    }
 
    public Test() {
        setPreferredSize(new Dimension(300,300));
    }
 
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g.create();
        Rectangle2D rectangleNotToDrawIn = new Rectangle2D.Double(100,100,20,30);
        Area outside = calculateRectOutside(rectangleNotToDrawIn);
        g2.setPaint(Color.white);
        g2.fillRect(0,getWidth(),getHeight());
        g2.setPaint(Color.black);
        g2.setClip(outside);
        g2.drawLine(0,getHeight());
 
    }
 
 
    private Area calculateRectOutside(Rectangle2D r) {
        Area outside = new Area(new Rectangle2D.Double(0,getHeight()));
        outside.subtract(new Area(r));
        return outside;
    }
 
}