有關重繪的完整程式碼如下：

package drawFrame;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Graphics;

import javax.swing.JFrame;

public class DrawFrame {
    public static void main(String[] args){
        DrawFrame df = new DrawFrame();
        df.showUI();
    }
    
 
public void showUI(){
        MyFrame jf = new MyFrame();
        jf.setSize(800,800);
        jf.setTitle("畫圖工具");
        jf.setLocationRelativeTo(null);
        jf.setDefaultCloseOperation(3);
        
        //新增流式佈局。
        FlowLayout flow = new FlowLayout(FlowLayout.LEFT);//設定對齊方式為左對齊，在括號裡面寫。
        
 
//上面只是建立這個物件，接下來要set一下。
        jf.setLayout(flow);
        
        DrawMouse mouse = new DrawMouse();
        jf.array = mouse.arr;
        
        String a[] = {"直線","圓","矩形","多邊形","三角形","曲線","點","精美的圖形","分形圖形","樹","康托爾集","謝賓斯基三角形"};
        Color ch[] = {Color.blue,Color.green};
        
        
 
for(int i=0;i<a.length;i++){
            javax.swing.JButton bh = new javax.swing.JButton(a[i]);  //新建物件？（新建這個按鈕？）
            jf.add(bh);                                              //在jf裡面add這個bh
            bh.addActionListener(mouse);                             //bh新增動作監聽器
        }
        
//        javax.swing.JButton jbu6 = new javax.swing.JButton("曲線");
//        jf.add(jbu6);
    
        for(int j=0;j<ch.length;j++){
            javax.swing.JButton s = new javax.swing.JButton();    //新建顏色按鈕？
            s.setBackground(ch[j]);                              //新增背景顏色？
            s.setPreferredSize(new Dimension(30,30));          //設定顏色按鈕的大小
            jf.add(s);                                        //jf裡面加這個s
            s.addActionListener(mouse);                            //給s新增動作監聽器
        }
        
//        javax.swing.JButton blue = new javax.swing.JButton();
        
        //設定按鈕背景色
        
//        blue.setBackground(Color.BLUE);
//        blue.setPreferredSize(new Dimension(30, 30));
//        jf.add(blue);
//        
//        javax.swing.JButton green = new javax.swing.JButton();
//        green.setBackground(Color.GREEN);
//        green.setPreferredSize(new Dimension(30,30));
//        jf.add(green);
    
        jf.setVisible(true);    //設定可見
        
        Graphics g =jf.getGraphics();
        
        jf.addMouseListener(mouse);
        mouse.gr = g;
        jf.addMouseMotionListener(mouse);
        mouse.gr = g;
        
        //上面DrawMouse裡面已經定義了一個mouse物件了，這裡直接用mouse.
        //因為DrawMouse同時監聽了 MouseListener,ActionListen兩種動作。
        
//        for(int j = 0;j < 6;j++){
//            b[j].addActionListener(mouse);
//        }
    
//        jbu.addActionListener(mouse);
    
    //    green.addActionListener(mouse);
    }
}

package drawFrame;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.Random;
import javax.swing.JButton;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;

public class DrawMouse implements MouseListener, ActionListener, MouseMotionListener {

public Graphics gr;
private int x1, x2, y1, y2;
private int m, n, p, q;
String ab;
Color color;   //剛才這裡遇到了一個問題，在drawShape裡面添加了color引數，但還是用不起來，這是因為，這裡定義的color跟下面的*行的color
                   //不是同一個東西，要怎樣才能是同一個東西呢？很簡單，把*行的Color color = jbu.getBackground();改成
                    //color = jbu.getBackground();就可以了。
Shape arr[] = new Shape[1000];
int index = 0;
public void actionPerformed(ActionEvent e) {
        if ("".equals(e.getActionCommand())) {
            JButton jbu = (JButton) e.getSource();
            color = jbu.getBackground();   //*
            gr.setColor(color);
        } 
        else {
            ab = e.getActionCommand();
            System.out.println("ab=" + ab);
        }
    }

public void mouseDragged(MouseEvent e) {
        
    }
public void mouseMoved(MouseEvent e) {

    }
public void mouseClicked(MouseEvent e) {

    }
public void mousePressed(MouseEvent e) {
        if (flag == 1) {   //這是畫三角形多邊形的，與這次重繪無關，不用管
            x1 = e.getX();
            y1 = e.getY();
        }
    }
public void mouseReleased(MouseEvent e) {
        if (flag == 1) {
            x2 = e.getX();
            y2 = e.getY();
        }
        else if (ab.equals("直線")) {
            gr.drawLine(x1, y1, x2, y2);
            Shape shape = new Shape(x1,y1,x2,y2,ab,color);
            arr[index++] = shape;
        }
        else if (ab.equals("圓")) {
            m = x1 < x2 ? x1 : x2;
            n = y1 < y2 ? y1 : y2;
            gr.drawOval(m, n, Math.abs(x2 - x1), Math.abs(y2 - y1));
            Shape shape = new Shape(x1,y1,x2,y2,ab,color);
            arr[index++] = shape;
        }
        else if (ab.equals("矩形")) {
            p = x1 < x2 ? x1 : x2;
            q = y1 < y2 ? y1 : y2;
            gr.drawRect(p, q, Math.abs(x2 - x1), Math.abs(y2 - y1));
            Shape shape = new Shape(x1,y1,x2,y2,ab,color);
            arr[index++] = shape;
        }
}
public void mouseEntered(MouseEvent e) {
        // System.out.println("進入");
    }

    public void mouseExited(MouseEvent e) {
        // System.out.println("退出");
    }
}

package drawFrame;
import java.awt.Graphics;
import javax.swing.JButton;
import java.awt.Color;
public class Shape {
    public int x1,y1,x2,y2;
    String name;
    Color color;
    public int m,n;
    public Shape(int xa,int ya,int xb,int yb,String n,Color co){
        x1 = xa;y1 = ya;
        x2 = xb;y2 = yb;
        name = n;color = co;
    }
    public void drawShape(Graphics g){
        m = x1 < x2 ? x1 : x2;
        n = y1 < y2 ? y1 : y2;
        switch(name){
        case "直線":
            g.setColor(color);
            g.drawLine(x1, y1, x2, y2);
            break;
        case "圓":
            g.setColor(color);
            g.drawOval(m, n, Math.abs(x2 - x1), Math.abs(y2 - y1));
            break;
        case "矩形":
            g.setColor(color);
            g.drawRect(m, n, Math.abs(x2 - x1), Math.abs(y2 - y1));
            break;
        }
    }
}    

package drawFrame;
import java.awt.Graphics;
import javax.swing.JFrame;

public class MyFrame extends JFrame{    //extends這裡是繼承的意思，這裡用了extends，在DrawFrame的showUI裡就可以把JFrame改成MyFrame了
    Shape array[] = null;
    public void paint(Graphics g){
        super.paint(g);
        for(int i = 0;i < array.length;i++){    //array.length表示這個陣列的長度
            Shape shape = array[i];
            if(shape != null){
                shape.drawShape(g);
            }
        }
    }
}