import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.ArrayList;

import javax.swing.JPanel;

public class MyPanel extends JPanel {
	private ArrayList<Point> point;

	public MyPanel() {
		point = new ArrayList<Point>();
		// Anonymous class.
		this.addMouseListener(new MouseAdapter() {
			public void mouseClicked(MouseEvent e) {
				// Check whether the left mouse button is clicked
				if (e.getButton() == MouseEvent.BUTTON1) {
					// store the point which been clicked
					point.add(e.getPoint());
					// get the coordinate
					System.out.println("(" + e.getX() + "," + e.getY() + ")");
				}

			}
		});
	}

	@Override
	protected void paintComponent(Graphics g) {
		// must clean the panel before drawing on it.
		super.paintComponent(g);
		g.setColor(Color.RED);
		for (int i = 0; i < point.size(); i++) {
			g.drawRect((int) point.get(i).getX(), (int) point.get(i).getY(), 1, 1);
			if (i > 0) {
				// connect next point
				g.drawLine((int) point.get(i).getX(), (int) point.get(i).getY(),
						(int) point.get(i - 1).getX(), (int) point.get(i - 1).getY());
			}
		}
		// draw the red square
		repaint();
	}
}