Drawing shapes does not work in graphics2D

Drawing shapes does not work in graphics2D

The below code is to display a triangle in applet.But it does not work for
me. If i pass Graphics g instead of Graphics2D g then it works fine.But i
want to know what the mistake i am doing while using Graphics g. I am new
to java and learning from some online tutorials. So please correct my
program and tell me what mistake i am doing.
import javax.swing.*;
import javax.swing.event.*;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class Vehicle extends JFrame {
final int WIDTH = 900;
int HEIGHT = 650;
public void init() {
setSize(WIDTH, HEIGHT);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setVisible(true);
}
public void paint(Graphics2D g) {
Graphics2D g2 = (Graphics2D) g;
Dimension d = getSize();
System.out.println(d);
int[] yPoints={150,250,250};
int[] xPoints={200,150,250};
g2.setColor(Color.green);
g2.drawPolygon(xPoints, yPoints, 3);
g2.drawRect(100, 100, 100, 100);
g2.setColor(Color.red);
g2.fillPolygon(xPoints, yPoints, 3);
}
public static void main(String[] args) {
Vehicle v= new Vehicle();
v.init();
}
}