图形画不出来（java）

Question

package draw;

import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;

public class DrawTest {
public static void main(String[] args) {
EventQueue.invokeLater(()->
{
JFrame frame = new DrawFrame();
frame.setTitle("DrawTest");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
});
}
}
/**
A frame that contains a panel with drawings
*/
class DrawFrame extends JFrame{
public DrawFrame() {
add(new DrawComponent());
pack();
}
}
/*
*A component that displays rectangle and ellipses.
*/
class DrawComponent extends JComponent {
private static final int DEFAULT_WIDTH = 400;
private static final int DEFAULT_HEIGHT = 400;

public void painComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D) g;

    //draw a rectangle

    double leftX = 100;
    double topY = 100;
    double width = 200;
    double heigh = 150;
    Rectangle2D rect = new Rectangle2D.Double(leftX,topY,width,heigh);
    g2.draw(rect);

    //draw a enclosed ellipse

    Ellipse2D ellipse = new Ellipse2D.Double();
    ellipse.setFrame(rect);
    g2.draw(ellipse);

    //draw a diagonal line

    g2.draw(new Line2D.Double(leftX,topY,width+leftX,heigh+topY));

    //draw a circle with same center

    double centerX = rect.getCenterX();
    double centerY = rect.getCenterY();
    double radius = 150;

    Ellipse2D circle = new Ellipse2D.Double();
    circle.setFrameFromCenter(centerX, centerY,centerX+radius,centerY+radius);
    g2.draw(circle);
    }
public Dimension getPreferredSize() {
    return new Dimension(DEFAULT_WIDTH,DEFAULT_HEIGHT);
}

}

以上是我的代码，我是从JAVA核心技术那本书上看来的，按理说像这种书一般不会出错。但我对了几遍发现并没有和他不一样的地方，自己也不是很懂，请前辈们指教。为什么图形就是画不出来呢

Answer 1

好吧我自己给自己回答好了。
把paintComponent()改成paint就可以了。