Java Graphics - 如何画一个三角形

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.geom.Path2D;
import java.awt.geom.Point2D;

import javax.swing.JFrame;
import javax.swing.JPanel;

public class Main {
  public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLayout(new BorderLayout());
    frame.add(new TestPane());
    frame.pack();
    frame.setVisible(true);
  }
}
class TestPane extends JPanel {
  TriangleShape triangleShape;
  Polygon poly;
  public TestPane() {
    triangleShape = new TriangleShape(new Point2D.Double(50, 0),
        new Point2D.Double(100, 100), new Point2D.Double(0, 100));
    poly = new Polygon(new int[] { 50, 100, 0 }, new int[] { 0, 100, 100 }, 3);
  }
  @Override
  public Dimension getPreferredSize() {
    return new Dimension(200, 200);
  }

  @Override
  protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g.create();
    g2d.setColor(Color.RED);
    g2d.fill(poly);

    g2d.setColor(Color.GREEN);
    g2d.translate(50, 100);
    g2d.fill(triangleShape);
    g2d.dispose();
  }
}
class TriangleShape extends Path2D.Double {
  public TriangleShape(Point2D... points) {
    moveTo(points[0].getX(), points[0].getY());
    lineTo(points[1].getX(), points[1].getY());
    lineTo(points[2].getX(), points[2].getY());
    closePath();
  }
}