import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.util.*;
import java.util.List;

public class RectanglePanel extends JLabel implements MouseListener {
	private List<Rectangle> toDraw;
	private Point lastClicked;
	public RectanglePanel() {
		super();
		this.addMouseListener(this);
		toDraw = new LinkedList<Rectangle>();
	}
	public void paintComponent(Graphics g) {
		super.paintComponent(g);
		for(Rectangle r : this.toDraw) {
			g.drawRect(r.x, r.y, r.width, r.height);
		}
	}
	public void mousePressed(MouseEvent me) {
	}
	public void mouseReleased(MouseEvent me) {
	}
	private static Rectangle createRectangle(Point from, Point to) {
		int x1 = (int)Math.min(from.getX(), to.getX());
		int y1 = (int)Math.min(from.getY(), to.getY());
		int x2 = (int)Math.max(from.getX(), to.getX());
		int y2 = (int)Math.max(from.getY(), to.getY());
		return new Rectangle(x1, y1, x2 - x1, y2 - y1);
	}
	public void mouseClicked(MouseEvent me) {
		if(lastClicked==null)
			lastClicked = me.getPoint();
		else {
			toDraw.add(createRectangle(lastClicked, me.getPoint()));
			lastClicked = null;
			this.invalidate();
			this.repaint();
			this.revalidate();
		}
	}
	public void mouseExited(MouseEvent me) { }
	public void mouseEntered(MouseEvent me) { }

	public static void main(String[] args) {
		JFrame f = new JFrame();
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		JPanel p = new JPanel(new BorderLayout());
		p.add(new RectanglePanel(), BorderLayout.CENTER);
		f.setContentPane(p);
		f.pack();
		f.setVisible(true);
	}
}