Vẽ tam giác

package vetamgiac;

/**
 *
 * @author thieumao
 */
import java.awt.event.*;
import javax.swing.*;

public class VeTamGiac extends JPanel implements MouseListener {

    int x1, x2, x3, y1, y2, y3;

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        frame.add(new VeTamGiac());
        frame.setSize(400, 400);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public VeTamGiac() {
        super();
        addMouseListener(this);
    }

    public void mouseClicked(MouseEvent e) {
    }

    public void mouseEntered(MouseEvent e) {
    }

    public void mouseExited(MouseEvent e) {
    }

    public void mouseReleased(MouseEvent e) {
        x1 = 100;
        y1 = 100;
        x2 = 200;
        y2 = 100;
        x3 = 200;
        y3 = 200;
        getGraphics().drawLine(x1, y1, x2, y2);
        getGraphics().drawLine(x2, y2, x3, y3);
        getGraphics().drawLine(x3, y3, x1, y1);
    }

    public void mousePressed(MouseEvent e) {
    }
}