请问为什么下面的程序画不出来矩形呢

请问为什么下面的程序画不出来矩形呢？

import java.util.*;
import java.applet.*;
import java.awt.event.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;

public class Try extends JFrame {
Frame f1;
Canvas cvs;
Graphics gf;
public Try() {
cvs = new Canvas();
cvs.setSize(200,200);
this.getContentPane().add(cvs,BorderLayout.CENTER);
this.pack();

gf = cvs.getGraphics();
gf.setColor(Color.WHITE);
gf.fillRect(0,0, 100,100);
gf.setColor(Color.BLUE);
gf.fillRect(0,0, 50,50);
}

    public static void main(String[] args) {
        JFrame dd= new Try();
        dd.setSize(300,300);
        dd.setVisible(true);
    }

} --------------------编程问答-------------------- 你有很多设置、换算的东西，可是。。。打印输出呢？？？

--------------------编程问答-------------------- 另一个类似的程序，也是得不到图画。

import java.util.*;
import java.applet.*;
import java.awt.event.*;
import java.awt.*;
import java.awt.image.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.awt.Graphics;
import java.awt.Color;

public class Try extends JFrame {
Frame f1;
Canvas cvs;
Graphics gf;
public Try() {
cvs = new Canvas();
cvs.setSize(200,200);
this.getContentPane().add(cvs,BorderLayout.CENTER);
this.pack();
cvs.setBackground(Color.BLACK);
gf = cvs.getGraphics();
gf.setColor(Color.yellow);
Image ig = createImage(this.getSize().width, this.getSize().height);
Graphics gh = ig.getGraphics();
gh.fillRect(0,0,100,100);
gh.setColor(Color.BLUE);
gh.fillRect(0,0,50,50);
cvs.getGraphics().drawImage(ig,0,0,this);
}

    public static void main(String[] args) {
        JFrame dd= new Try();
        dd.setSize(300,300);
        dd.setVisible(true);
    }

} --------------------编程问答-------------------- 你有很多设置、换算的东西，可是。。。打印输出呢？？？
=============
请问如何输出图画？ --------------------编程问答-------------------- import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.geom.Rectangle2D;
/**
* Displays a JFrame and draws a ractangle on it using the Java 2D Graphics API
*
* @author www.javadb.com
*/
public class Java2DFrame extends javax.swing.JFrame {

    /**
     * Creates a new instance of Java2DFrame
     */
    public Java2DFrame() {
        initComponents();
    }

    /**
     * This is the method where the rectangle is drawn.
     *
     * @param g The graphics object
     */
    public void paint(Graphics g) {
        Graphics2D graphics2 = (Graphics2D) g;
        Rectangle2D rectangle = new Rectangle2D.Float(100, 100, 240, 160);
        graphics2.draw(rectangle);
    }

    // <editor-fold defaultstate="collapsed" desc=" Generated Code ">
    private void initComponents() {

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        org.jdesktop.layout.GroupLayout layout = new org.jdesktop.layout.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(0, 400, Short.MAX_VALUE)
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(org.jdesktop.layout.GroupLayout.LEADING)
            .add(0, 300, Short.MAX_VALUE)
        );
        pack();
    }// </editor-fold>

    /**
     * Starts the program
     *
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new Java2DFrame().setVisible(true);
            }
        });
    }
}

--------------------编程问答--------------------   /**
   * This is the method where the rectangle is drawn.
   *
   * @param g The graphics object
   */
   public void paint(Graphics g) {
   Graphics2D graphics2 = (Graphics2D) g;
   Rectangle2D rectangle = new Rectangle2D.Float(100, 100, 240, 160);
   graphics2.draw(rectangle);
  }

补充：Java ,  Java SE