製作一個畫圖介面主要分為四個步驟

一、 建立一個圖畫介面

      利用Java 的 swing，awt 提供的相關內容進行繪畫

二、 處理事件

       事件監聽機制

三. 編寫事件處理的具體方法

四. 實現重繪

     建立一個可以儲存相關資訊的類（Shape）來記錄資訊，在建立Shape[] array陣列來記錄資料

1.   Drawing 主要用於實現畫圖介面的繪畫

import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.Graphics2D;

import javax.swing.JComboBox;
import javax.swing.JFrame;

public class Drawing extends JFrame{

	public Shape[] array = new Shape[1000];  //利用陣列將資料存起來
	
	public static void main(String[] args) {
		
		Drawing draw = new Drawing();
		draw.InitUI();

	}
	public void InitUI() {
		setTitle("畫圖介面");
		setLayout(new FlowLayout());
		setSize(800,800);
		setLocationRelativeTo(null);
		setDefaultCloseOperation(3);
		
		//定義圖型下拉框    1. 用一個數組記錄下拉框中的內容
		String[] typeArray = {"直線","矩形","圓","3D矩形","圖片","文字Hello","等腰三角形","五角星","任意多邊形","立方體","鉛筆","噴槍","橡皮擦"};
		JComboBox<String> cbType = new JComboBox<String>(typeArray);    
		cbType.setName("圖型");    //給下拉框取名字，以便區分點選的 圖型 、 顏色  、粗細中哪一個下拉框
		add(cbType); 
		
		//定義顏色下拉框    1. 用一個數組記錄下拉框中的內容
		String[] colorArray = {"紅色","綠色","藍色"};
		JComboBox<String> cbColor = new JComboBox<String>(colorArray);
		cbColor.setName("顏色");   //給下拉框取名字，以便區分點選的 圖型 、 顏色  、粗細中哪一個下拉框
		add(cbColor);
		
		//定義粗細下拉框    1. 用一個數組記錄下拉框中的內容
		String[] strokeArray = {"1","3","5"};
		JComboBox<String> cbStroke = new JComboBox<String>(strokeArray);
		cbStroke.setName("粗細");   //給下拉框取名字，以便區分點選的 圖型 、 顏色  、粗細中哪一個下拉框
		add(cbStroke);
		
		setVisible(true);
		
		Graphics g = getGraphics();    //畫筆一定要在setVisible（boolean)方法後定義，否則 g = null;
		
		DrawingListener dl = new DrawingListener((Graphics2D)g,array);
		cbType.addActionListener(dl);     //處理下拉框 圖型中的 事件
		cbColor.addActionListener(dl);    //處理下拉框 顏色中的 事件
		cbStroke.addActionListener(dl);   //處理下拉框 粗細中的 事件
		
		addMouseListener(dl);        
		//處理在視窗上發生的動作
		//主要是滑鼠的點選（mouseClicked），按下（mousePressed），釋放（ mouseReleased），進入（mouseEntered），離開（mouseExited）
		addMouseMotionListener(dl);  
		//處理在視窗上發生的動作
		//滑鼠的拖動（mouseDragged），移動（mouseMoved）
		
		
	}
	
	public void paint(Graphics g) {    //Drawing類繼承看JFrame，這裡重寫JFrame類中的paint()方法，以實現重繪
		
		super.paint(g);   //呼叫父類中的paint方法，以畫出視窗和下拉框
		System.out.println("重繪窗體和元件");
		 
		//將視窗重繪前已經畫的內容繪畫一遍，以實現視窗重繪後內容的復原
		for(int i = 0;i < array.length;i++)
			if(array[i] != null)
				array[i].draw((Graphics2D) g);
	}
	

}
 

2.DrawingListener 主要用於處理事件

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.awt.event.MouseMotionListener;
import java.util.Scanner;

import javax.swing.JComboBox;
import javax.swing.JFrame;

/**  DrawingListener 繼承JFrame以得到畫筆，Toolkit
  *  繼承ActionListener,MouseListener,MouseMotionListener  事件接聽介面
  *  */
public class DrawingListener extends JFrame implements ActionListener,MouseListener,MouseMotionListener {
	
	 private String type = "直線";
	 private Color color = Color.red;
	 private float stroke = 1;
 	 private Graphics2D g;
	 private int x1,y1,x2,y2;

     int fx,fy,lx,ly;    //fx，fy記錄起點的座標，lx、ly記錄上一個點的座標
 
	 private boolean sign = true;  //記錄是否為起點（多邊形）
	 public Shape[] array ;  
	 int index;

		/**
		 * 構造方法
		 * g是從窗體上傳遞過來的畫筆物件
		 * array 將陣列傳過來以儲存資料
		 */
	 public DrawingListener(Graphics2D g,Shape[] array) {  
		 this.g = g;
		 this.array = array;  
	 }
	 
	 public void actionPerformed(ActionEvent e) {
	     JComboBox<String> cb = (JComboBox<String>)e.getSource();  //獲取事件源物件
	     String str = cb.getName();    //獲取下拉框的名字，根據name屬性來做判斷
	     if(str.equals("圖型")) {       
	    	 type = cb.getSelectedItem().toString();   //獲取選擇的圖形資訊
	    	 
	     }else if(str.equals("顏色")) {        //獲取選擇的顏色資訊
	    	 if(cb.getSelectedItem().toString().equals("紅色"))  
	    		 color = Color.RED;
	    	 else if(cb.getSelectedItem().toString().equals("綠色"))
	    		 color = Color.GREEN;
	    	 else if(cb.getSelectedItem().toString().equals("藍色"))
	    		 color = Color.BLUE;
	     }else if(str.equals("粗細")) {
	    	     //Integer.parseInt(String) 將字串轉化為整型
	    	      stroke = (float)Integer.parseInt(cb.getSelectedItem().toString());
	     }
	     
	 }
	 
	    public void mouseClicked(MouseEvent e) {  //滑鼠點選呼叫的方法
	    	
	    };

	    
	   
	    public void mousePressed(MouseEvent e) {  //滑鼠按下呼叫的方法
	    	x1 = e.getX();     //得到按下時的座標
	    	y1 = e.getY();
	    	g.setColor(color);  //設定線條粗細
	    	g.setStroke(new BasicStroke(stroke));  //設定粗細，注意setStroke方法只在Graphics2D中有，在Graphics中沒有
	    	                                       //所以你的畫筆g的型別為Graphics2D
	    }

	    public void mouseReleased(MouseEvent e) {  //滑鼠（按下）釋放時呼叫的方法
	    	x2 = e.getX();  //得到釋放時的座標
	    	y2 = e.getY();
	    	
	    	//我這裡是想將做需要的資訊存到array陣列中，在呼叫Shape中的draw方法
	    	if(type.equals("直線")||type.equals("矩形")||type.equals("圓")||type.equals("3D矩形")||type.equals("文字Hello")||type.equals("等腰三角形")||type.equals("五角星")|type.equals("立方體")) {
	    		 
	    		 Shape s = new Shape(x1,y1,x2,y2,color,stroke,type);   //儲存資料
	    		 if(index < 1000)    //當儲存的資料超過1000後將不再儲存
	    			 array[index++] = s;
	    		 s.draw(g);
	    		 
	    	}else if(type.equals("圖片")) {
	    		 Toolkit tool = this.getToolkit();   
	   		       //這個this應該指向JFrame，JPanel，所以我在治理繼承了JFrame類
	   		     Image image = tool.getImage("C:\\Users\\ASUS\\Desktop\\p2.png");   //給image賦值
	    		 Shape s = new Shape(x1,y1,x2,y2,color,stroke,type,image);
	    		 if(index < 1000)
	    			 array[index++] = s;
	    		 s.draw(g);
	    		 
	    	 }else if(type.equals("任意多邊形")){

	       		 if(sign) {   //當此時畫的是任意多邊形的第一條線
	       			 fx = x1;  fy = y1;   //fx，fy記錄起點的座標，lx、ly記錄上一個點的座標
	       			 lx = x1;  ly = y1;
	       			Shape s = new Shape(lx,ly,x2,y2,color,stroke,type);   //直接儲存需要畫的直線
		    		 if(index < 1000)
		    			 array[index++] = s;
		    		 s.draw(g);
	       			 sign = false;     //sign = false 即接下來畫的不是任意多邊形的第一條線
	       		 }else {  //畫的不是任意多邊形的第一條線
	       			 
	       			 if(x2 > fx-9 && x2 < fx+9 && y2 > fy-9 && y2 < fy+9) {  //判斷此時釋放的位置是不是任意多邊形結束的位置
	       				Shape s = new Shape(lx,ly,fx,fy,color,stroke,type);     
			    		 if(index < 1000)
			    			 array[index++] = s;
			    		 s.draw(g);

	       				 sign = true;
	       			 }
	       			 else {   //釋放位置不是終止位置時
	       				Shape s = new Shape(lx,ly,x2,y2,color,stroke,type);
		    		 if(index < 1000)
		    			 array[index++] = s;
		    		 s.draw(g);
	       			 }
	       		 }
	       		 lx = x2;  ly = y2;
	    	 }
	    	
	    }

	   
	    public void mouseEntered(MouseEvent e) {   //滑鼠進入是呼叫呃方法
	    	
	    }

	    
	    public void mouseExited(MouseEvent e) {   //滑鼠離開時呼叫的方法
	    	
	    }
	    
	    public void mouseDragged(MouseEvent e) {   //滑鼠拖動時呼叫的方法
	    	if(type.equals("鉛筆")) {  //實現鉛筆
	    	   x2 = e.getX();
	    	   y2 = e.getY();
	    	   Shape s = new Shape(x1,y1,x2,y2,color,stroke,type);
	    	   if(index < 1000)
	    		   array[index++] = s;
	    	   s.draw(g);
	    	   x1 = x2;
	    	   y1 = y2;
	    	}else if(type.equals("噴槍")) {   //實現噴槍
	    		x2 = e.getX();
	    		y2 = e.getY();
	    		Shape s = new Shape(x2,y2,color,stroke,type);
	    		if(index < 1000)
		    		   array[index++] = s;
		    	  s.draw(g);
	    		
	    	}else if(type.equals("橡皮擦")) {   //實現橡皮擦
	    		x2 = e.getX();
	    		y2 = e.getY();
	    		Shape s = new Shape(x2,y2,color,stroke,type); 
	    		if(index < 1000)
		    		   array[index++] = s;
		    	  s.draw(g);
	    	}
	    }
	    
	    public void mouseMoved(MouseEvent e) {   //滑鼠移動是呼叫的方法
	    	
	    }

}
 

3. Shape 主要用於儲存資料，實現重繪

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.util.Random;

import javax.swing.JFrame;

public class Shape extends JFrame{
	public int x1,y1,x2,y2;
	public Color color;
	public float stroke;
	public String type;
	public Image img;
	public Random rand = new Random();
	
/*
 * 建構函式的過載
 */
	public Shape(int x1,int y1,int x2,int y2,Color color,float strock,String type) {  
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
		this.color = color;
		this.stroke = strock;
		this.type = type;
	}
	
	public Shape(int x1,int y1,int x2,int y2,Color color,float stroke,String type,Image img) { 
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
		this.color = color;
		this.stroke = stroke;
		this.type = type;
		this.img = img;
	}
	
	public Shape(int x2,int y2,Color color,float stroke,String type) {
		this.x2 = x2;
		this.y2 = y2;
		this.color = color;
		this.stroke = stroke;
		this.type = type;
	}
	
	public void draw(Graphics2D g) {  //畫圖
		g.setColor(color);
		g.setStroke(new BasicStroke(stroke));
		if(type.equals("直線")) {
   		 g.drawLine(x1, y1, x2, y2);	

   	}
   	 else if(type.equals("矩形")) {
   		 
   		 MyDrawRect myDrawRect = new MyDrawRect(g);
  		 myDrawRect.drawRect(x1, y1, x2, y2);  //自定義畫矩形的方法，以使之不必侷限於只能往右下角畫矩形
   	 }
   	 else if(type.equals("圓")) {
   		 
   		 MyDrawCircle myDrawCircle = new MyDrawCircle(g);
   		 myDrawCircle.drawCircle(x1, y1, x2, y2);      //自定義畫圓的方法，以使之不必侷限於只能往右下角畫圓
   		 
   	 }
   	 else if(type.equals("3D矩形")) {
   		 
   		 MyDraw3DRect myDraw3DRect = new MyDraw3DRect(g);
   		 myDraw3DRect.draw3DRect(x1, y1, x2, y2);    //自定義畫3D矩形的方法，以使之不必侷限於只能往右下角畫3D矩形
   		 
   	 }else if(type.equals("圖片")) {
   		 
   		 MyDrawImag myDrawImage = new MyDrawImag(g);
   		 myDrawImage.drawImage(x1,y1,x2,y2,img);    //自定義畫圖片的方法，以使之不必侷限於只能往右下角畫圖片
   		 
   	 }else if(type.equals("文字Hello")) {    
   		 String str = "Hello"; 
   	     g.drawString(str, x1, y1);
   		 
   	 }else if(type.equals("等腰三角形")) {
   		 
   		 g.drawLine((x1+x2)/2, y1, x1, y2);
   		 g.drawLine(x1, y2, x2, y2);
   		 g.drawLine((x1+x2)/2, y1, x2, y2);
   		 
   	 }else if(type.equals("五角星")) {
   		 
   		 MyDrawPentagram myDrawPentagram = new MyDrawPentagram(g);
   		 myDrawPentagram.drawPentagram(x1, y1, x2, y2);   //自定義畫五角星的方法，以使之不必侷限於只能往右下角畫圖片
   		  
   	 }else if(type.equals("任意多邊形")) { 
   		 g.drawLine(x1, y1, x2, y2);    //因為在DrawingListener類中已經進行了相關資料的處理，所以這裡只需畫直線即可
   		 
   	 }else if(type.equals("立方體")) {
   		 MyDrawCube myDrawCube = new MyDrawCube(g);
   		 myDrawCube.drawCube(x1,y1,x2,y2);   //自定義畫立方體的方法，以使之不必侷限於只能往右下角畫圖片
   		 
   	 }else if(type.equals("鉛筆")) {
   		 
		 g.drawLine(x1, y1, x2, y2);    //鉛筆實際上就是在畫直線而已，只不過兩點之間的距離很短
		 
	 }else if(type.equals("噴槍")) {
		 
		  for(int num = 0;num < 25;num++) {
			  x1 = rand.nextInt(10)+x2-5;   //在以（x2，y2）為中點，長為10的正方形中畫點
			  y1 = rand.nextInt(10)+y2-5;
			  g.drawLine(x1,y1,x1,y2);
		  }
		  
	 }else if(type.equals("橡皮擦")) {   
		 g.clearRect(x2-2, y2-2, 15, 15);   //用clearRect方法畫與背景顏色一樣的矩形
	 }
   	
		
	}
	
	

}
 

4. 畫3D矩形

import java.awt.Graphics;

/*
 * 畫3D矩形
 */
public class MyDraw3DRect {
	private Graphics g;
	int x1,y1,x2,y2;
	
	MyDraw3DRect(Graphics g){
		this.g = g;
	}
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	public void draw3DRect(int x1,int y1,int x2,int y2) {
		setXY(x1,y1,x2,y2);
		//區分x2，y2相對x1，y1的位置
		if(x2 < x1 && y2 <y1)         //左上
			g.draw3DRect(x2, y2, x1-x2, y1-y2,true);   //直接用draw3DRect()方法即可
		else if(x2 > x1 && y2 < y1)   //右上
			g.draw3DRect(x1, y2, x2-x1, y1-y2,true);
		else if(x2 < x1 && y2 > y1)   //左下
			g.draw3DRect(x2, y1, x1-x2, y2-y1,true);
		else                          //右下
			g.draw3DRect(x1, y1, x2-x1, y2-y1,true);
	}

}

5. 畫圓

import java.awt.Graphics;

public class MyDrawCircle {
	private Graphics g;
	int x1,y1,x2,y2;
	int d;
	StrictMath math;
	
	MyDrawCircle(Graphics g){
		this.g = g;
	}
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	public void drawCircle(int x1,int y1,int x2,int y2) {
		setXY(x1,y1,x2,y2);
		if(x2 < x1 && y2 <y1) {
			d = (int)math.sqrt(math.pow(x1-x2, 2)+math.pow(y1-y2, 2));
			g.drawOval(((x1+x2)/2)-d/2, ((y1+y2)/2)-d/2, d, d);
		}
		else if(x2 > x1 && y2 < y1) {
			d = (int)math.sqrt(math.pow(x2-x1, 2)+math.pow(y1-y2, 2));
			g.drawOval(((x1+x2)/2)-d/2, ((y1+y2)/2)-d/2, d, d);
		}
		else if(x2 < x1 && y2 > y1) {
			d = (int)math.sqrt(math.pow(x1-x2, 2)+math.pow(y2-y1, 2));
			g.drawOval(((x1+x2)/2)-d/2, ((y1+y2)/2)-d/2, d, d);
		}
		else {
			d = (int)math.sqrt(math.pow(x2-x1, 2)+math.pow(y2-y1, 2));
			g.drawOval(((x1+x2)/2)-d/2, ((y1+y2)/2)-d/2, d, d);
		}
	}

}

6. 畫立方體（其實此處畫的哪裡可以單獨分出來為一個方法）

import java.awt.Graphics;

/*
 * 畫立方體
 */
public class MyDrawCube {
	private Graphics g;
	int x1,y1,x2,y2;
	
	MyDrawCube(Graphics g){
		this.g = g;
	}
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	/*
	 * 畫立方體的虛線
	 */
	public void drawDashedShu(int x1,int y1,int x2,int y2) {  // 畫豎虛線
		g.drawLine(x1, y1, x1, y1+(y2-y1)/11);
		g.drawLine(x1, y1+((y2-y1)*2)/11, x1, y1+((y2-y1)*3	)/11);
		g.drawLine(x1, y1+((y2-y1)*4)/11, x1, y1+((y2-y1)*5)/11);
		g.drawLine(x1, y1+((y2-y1)*6)/11, x1, y1+((y2-y1)*7)/11);
		g.drawLine(x1, y1+((y2-y1)*8)/11, x1, y1+((y2-y1)*9)/11);
		g.drawLine(x1, y1+((y2-y1)*10)/11, x1, y2);
	}
	
	public void drawDashedHeng(int x1,int y1,int x2,int y2) {   //畫橫虛線
		g.drawLine(x1, y1, x1+((x2-x1)*1)/11, y1);
		g.drawLine(x1+((x2-x1)*2)/11, y1,x1+((x2-x1)*3)/11, y2);
		g.drawLine(x1+((x2-x1)*4)/11, y1, x1+((x2-x1)*5)/11, y2);
		g.drawLine(x1+((x2-x1)*6)/11, y1, x1+((x2-x1)*7)/11, y2);
		g.drawLine(x1+((x2-x1)*8)/11, y1, x1+((x2-x1)*9)/11, y2);
		g.drawLine(x1+((x2-x1)*10)/11, y1,x2, y2);
		
	}
	
	public void drawDashedXie(int x1,int y1,int x2,int y2) {    //畫斜虛線
		g.drawLine(x1, y1, x1+((x2-x1)*1)/7, y2+((y1-y2)*6)/7);
		g.drawLine(x1+((x2-x1)*2)/7, y2+((y1-y2)*5)/7, x1+((x2-x1)*3)/7, y2+((y1-y2)*4)/7);
		g.drawLine(x1+((x2-x1)*4)/7, y2+((y1-y2)*3)/7, x1+((x2-x1)*5)/7, y2+((y1-y2)*2)/7);
		g.drawLine(x1+((x2-x1)*6)/7, y2+((y1-y2)*1)/7, x2, y2);
	}
	
	public void drawCube(int x1,int y1,int x2,int y2) {    //畫立方體
		setXY(x1,y1,x2,y2);
		int w,h;
		if(x2 < x1 && y2 <y1) {     //左上角
			w = (x1-x2)/4;  h = (y1-y2)/4;
			g.drawLine(x2+w, y2, x1, y2);     //橫
			g.drawLine(x2, y2+h, x1-w, y2+h);
			g.drawLine(x2, y1, x1-w, y1);
			drawDashedHeng(x2+w,y1-h,x1,y1-h);
			g.drawLine(x2, y2+h, x2, y1);    //豎
			g.drawLine(x1-w, y2+h, x1-w, y1);
			g.drawLine(x1, y2, x1, y1-h);
			drawDashedShu(x2+w,y2,x2+w,y1-h);
			g.drawLine(x2, y2+h, x2+w, y2);   //斜
			g.drawLine(x1-w, y2+h, x1, y2);
			g.drawLine(x1-w, y1, x1, y1-h);
			drawDashedXie(x2,y1,x2+w,y1-h);
		}
		else if(x2 > x1 && y2 < y1) {     //右上角
			w = (x2-x1)/4;  h = (y1-y2)/4;
			g.drawLine(x1+w, y2, x2, y2);
			g.drawLine(x1, y2+h, x2-w, y2+h);
			g.drawLine(x1, y1, x2-w, y1);
			drawDashedHeng(x1+w,y1-h,x2,y1-h);
			g.drawLine(x1, y2+h, x1, y1);
			g.drawLine(x2-w, y2+h, x2-w, y1);
			g.drawLine(x2, y2, x2, y1-h);
			drawDashedShu(x1+w,y2,x1+w,y1-h);
			g.drawLine(x1, y2+h, x1+w, y2);
			g.drawLine(x2-w, y2+h, x2, y2);
			g.drawLine(x2-w, y1, x2, y1-h);
			drawDashedXie(x1,y1,x1+w,y1-h);
		}
		else if(x2 < x1 && y2 > y1) {     //左下角
			w = (x1-x2)/4;  h = (y2-y1)/4;
			g.drawLine(x2+w, y1, x1, y1);
			g.drawLine(x2, y1+h, x1-w, y1+h);
			g.drawLine(x2, y2, x1-w, y2);
			drawDashedHeng(x2+w,y2-h,x1,y2-h);
			g.drawLine(x2, y1+h, x2, y2);
			g.drawLine(x1-w, y1+h, x1-w, y2);
			g.drawLine(x1, y1, x1, y2-h);
			drawDashedShu(x2+w,y1,x2+w,y2-h);
			g.drawLine(x2, y1+h, x2+w, y1);
			g.drawLine(x1-w, y1+h, x1, y1);
			g.drawLine(x1-w, y2, x1, y2-h);
			drawDashedXie(x2,y2,x2+w,y2-h);
		}
		else {                             //右下角
			w = (x2-x1)/4;  h = (y2-y1)/4;
			g.drawLine(x1+w, y1, x2, y1);
			g.drawLine(x1, y1+h, x2-w, y1+h);
			g.drawLine(x1, y2, x2-w, y2);
			drawDashedHeng(x1+w,y2-h,x2,y2-h);
			g.drawLine(x1, y1+h, x1, y2);
			g.drawLine(x2-w, y1+h, x2-w, y2);
			g.drawLine(x2, y1, x2, y2-h);
			drawDashedShu(x1+w,y1,x1+w,y2-h);
			g.drawLine(x1, y1+h, x1+w, y1);
			g.drawLine(x2-w, y1+h, x2, y1);
			g.drawLine(x2-w, y2, x2, y2-h);
			drawDashedXie(x1,y2,x1+w,y2-h);
		}
	}
}

7. 畫圖

import java.awt.Graphics;
import java.awt.Image;
import java.awt.Toolkit;

import javax.swing.JFrame;
/*
 * 畫圖
 */
public class MyDrawImag extends JFrame{

	private Graphics g;
	private int x1,y1,x2,y2;
	private Observer observer;

	//Image img = new Image("C:\\Users\\ASUS\\Desktop\\p2.png");  是錯誤的，Image不能夠由於例項化
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	
	public MyDrawImag(Graphics g) {
		this.g = g;
	}
	
	public void drawImage(int x1,int y1,int x2,int y2,Image image) {
		setXY(x1,y1,x2,y2);
		if(x2 < x1 && y2 <y1)
			g.drawImage(image, x2, y2, x1-x2, y1-y2, observer);
		else if(x2 > x1 && y2 < y1)
			g.drawImage(image,x1, y2, x2-x1, y1-y2,observer);
		else if(x2 < x1 && y2 > y1)
			g.drawImage(image,x2, y1, x1-x2, y2-y1,observer);
		else
			g.drawImage(image,x1, y1, x2-x1, y2-y1,observer);
	}
}

8. 畫五角星

import java.awt.Graphics;
/*
 * 畫五角星
 */
public class MyDrawPentagram {
	private Graphics g;
	int x1,y1,x2,y2;
	int w,h;   //記錄寬，高
	int a1X,a1Y,a2X,a2Y,a3X,a3Y,a4X,a4Y,a5X,a5Y,a6X,a6Y,a7X,a7Y,a8X,a8Y,a9X,a9Y,a10X,a10Y;  //記錄五角星的每個角
	
	MyDrawPentagram(Graphics g){
		this.g = g;
	}
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	public void Line() {
		g.drawLine(a1X, a1Y, a2X,a2Y);
		g.drawLine(a2X, a2Y, a3X,a3Y);
		g.drawLine(a3X, a3Y, a4X,a4Y);
		g.drawLine(a4X, a4Y, a5X,a5Y);
		g.drawLine(a5X, a5Y, a6X,a6Y);
		g.drawLine(a6X, a6Y, a7X,a7Y);
		g.drawLine(a7X, a7Y, a8X,a8Y);
		g.drawLine(a8X, a8Y, a9X,a9Y);
		g.drawLine(a9X, a9Y, a10X,a10Y);
		g.drawLine(a10X, a10Y, a1X,a1Y);
	}
	public void drawPentagram(int x1,int y1,int x2,int y2) {
		setXY(x1,y1,x2,y2);
		
		if(x2 < x1 && y2 <y1) {
			w = x1-x2; h = y1-y2;
			a1X = x2+w/2;       a1Y = y2;
			a2X = x2+(w*3)/5;   a2Y = y2+(h*2)/5;
			a3X = x1;           a3Y = y2+(h*2)/5;
			a4X = x2+(w*2)/3;   a4Y = y2+(h*2)/3;
			a5X = x2+(w*4)/5;   a5Y = y1;
			a6X = x2+w/2;       a6Y = y2+(h*4)/5;
			a7X = x2+w/5;       a7Y = y1;
			a8X = x2+w/3;       a8Y = y2+(h*2)/3;
			a9X = x2;           a9Y = y2+(h*2)/5;
			a10X = x2+(w*2)/5;  a10Y = y2+(h*2)/5;
			Line();
		}
		else if(x2 > x1 && y2 < y1) {
			w = x2-x1; h = y1-y2;
			a1X = x1+w/2;       a1Y = y2;
			a2X = x1+(w*3)/5;   a2Y = y2+(h*2)/5;
			a3X = x2;           a3Y = y2+(h*2)/5;
			a4X = x1+(w*2)/3;   a4Y = y2+(h*2)/3;
			a5X = x1+(w*4)/5;   a5Y = y1;
			a6X = x1+w/2;       a6Y = y2+(h*4)/5;
			a7X = x1+w/5;       a7Y = y1;
			a8X = x1+w/3;       a8Y = y2+(h*2)/3;
			a9X = x1;           a9Y = y2+(h*2)/5;
			a10X = x1+(w*2)/5;  a10Y = y2+(h*2)/5;
			Line();
		}
		else if(x2 < x1 && y2 > y1) {
			w = x1-x2; h = y2-y1;
			a1X = x2+w/2;       a1Y = y1;
			a2X = x2+(w*3)/5;   a2Y = y1+(h*2)/5;
			a3X = x1;           a3Y = y1+(h*2)/5;
			a4X = x2+(w*2)/3;   a4Y = y1+(h*2)/3;
			a5X = x2+(w*4)/5;   a5Y = y2;
			a6X = x2+w/2;       a6Y = y1+(h*4)/5;
			a7X = x2+w/5;       a7Y = y2;
			a8X = x2+w/3;       a8Y = y1+(h*2)/3;
			a9X = x2;           a9Y = y1+(h*2)/5;
			a10X = x2+(w*2)/5;  a10Y = y1+(h*2)/5;
			Line();
		}
		else {
			w = x2-x1; h = y2-y1;
			a1X = x1+w/2;       a1Y = y1;
			a2X = x1+(w*3)/5;   a2Y = y1+(h*2)/5;
			a3X = x2;           a3Y = y1+(h*2)/5;
			a4X = x1+(w*2)/3;   a4Y = y1+(h*2)/3;
			a5X = x1+(w*4)/5;   a5Y = y2;
			a6X = x1+w/2;       a6Y = y1+(h*4)/5;
			a7X = x1+w/5;       a7Y = y2;
			a8X = x1+w/3;       a8Y = y1+(h*2)/3;
			a9X = x1;           a9Y = y1+(h*2)/5;
			a10X = x1+(w*2)/5;  a10Y = y1+(h*2)/5;
			Line();
		}
	}
}

9.畫矩形

import java.awt.Graphics;
/*
 * 畫矩形
 */
public class MyDrawRect {
	private Graphics g;
	int x1,y1,x2,y2;
	
	MyDrawRect(Graphics g){
		this.g = g;
	}
	
	public void setXY(int x1,int y1,int x2,int y2) {
		this.x1 = x1;
		this.y1 = y1;
		this.x2 = x2;
		this.y2 = y2;
	}
	public void drawRect(int x1,int y1,int x2,int y2) {
		setXY(x1,y1,x2,y2);
		if(x2 < x1 && y2 <y1)
			g.drawRect(x2, y2, x1-x2, y1-y2);
		else if(x2 > x1 && y2 < y1)
			g.drawRect(x1, y2, x2-x1, y1-y2);
		else if(x2 < x1 && y2 > y1)
			g.drawRect(x2, y1, x1-x2, y2-y1);
		else
			g.drawRect(x1, y1, x2-x1, y2-y1);
	}

}