Java学习笔记(五)：在JFrame中用Graphics类实现画板

清疚 2022-04-23 05:06 18阅读 0赞

## 一、画板功能 ##

*  实现一个可以选择画直线，矩形、圆、三角形、多边形等可改变颜色的图形的画板
 *  事件监听器和重绘原理

## 二、初步实现 ##

简单粗暴的实现画笔功能：  
监听器+画板界面  
`class SampleDraw:`

*  实现的是画笔界面显示，包含了各个按钮（button），画笔（Graphics）等。
 *  要注意的是画笔要放在界面可见的后面

package com.Graphics;
    
    public class SampleDraw {
        
    	public static void main(String [] args){
        
    		SampleDraw draw=new SampleDraw();
    		draw.showUI();
    	}
    	public void showUI(){
        
    		javax.swing.JFrame jf=new javax.swing.JFrame();
    		jf.setTitle("简单画板");
    		jf.setSize(600, 500);
    		jf.setResizable(false);//界面不可改变大小
    		jf.setDefaultCloseOperation(3);//关闭时退出程序
    		jf.setLocationRelativeTo(null);//居中显示
    		//流式布局
    		java.awt.FlowLayout flow=new java.awt.FlowLayout();
    		jf.setLayout(flow);
    		
    		
    		javax.swing.JButton line=new javax.swing.JButton("直线");
    		javax.swing.JButton rect=new javax.swing.JButton("矩形");
    		javax.swing.JButton arc=new javax.swing.JButton("圆");
    		javax.swing.JButton text=new javax.swing.JButton("TEXT");
    		javax.swing.JButton san=new javax.swing.JButton("三角形");
    		javax.swing.JButton xpc=new javax.swing.JButton("橡皮擦");
    		javax.swing.JButton dbx=new javax.swing.JButton("多边形");
    		javax.swing.JButton fs=new javax.swing.JButton("放射直线");
    		javax.swing.JButton color1=new javax.swing.JButton("green");
    		javax.swing.JButton color2=new javax.swing.JButton("blue");
    		javax.swing.JButton color3=new javax.swing.JButton("red");
    		jf.add(line);//划线按钮
    		jf.add(rect);//矩形按钮
    		jf.add(arc);//圆形按钮
    		jf.add(text);//文本按钮
    		jf.add(san);//三角形按钮
    		jf.add(dbx);//多边形按钮
    		jf.add(xpc);//橡皮擦按钮
    		jf.add(fs);
    		jf.add(color1);
    		jf.add(color2);
    		jf.add(color3);
    		color1.setBackground(java.awt.Color.green);
    		color2.setBackground(java.awt.Color.blue);
    		color3.setBackground(java.awt.Color.red);
    		java.awt.Container pane=jf.getContentPane();
    		pane.setBackground(java.awt.Color.white);	
    		jf.setVisible(true);//可见 可见要加在画笔前面
    
    	
    		//从窗体上获取画笔
    		//获取窗体在屏幕上占据的区域，这块区域是可以改变颜色的
    		java.awt.Graphics g=jf.getGraphics();//画笔，一定要放在可见之后
    		DrawListener dlis=new DrawListener(g);
    		
    		
    		
    		//jf.setBackground(java.awt.Color.white);
    		line.addActionListener(dlis);
    		rect.addActionListener(dlis);
    		arc.addActionListener(dlis);
    		text.addActionListener(dlis);
    		san.addActionListener(dlis);
    		xpc.addActionListener(dlis);
    		dbx.addActionListener(dlis);
    		fs.addActionListener(dlis);
    		color1.addActionListener(dlis);
    		color2.addActionListener(dlis);
    		color3.addActionListener(dlis);
    		jf.addMouseListener(dlis);//鼠标监听
    		jf.addMouseMotionListener(dlis);
    		
    	}
    	
    }

监听事件：  
`class DrawListener:`  
根据按钮的e.getActionCommand()判断选择的是画什么东西，三角形是先画一条边再话一个点，点与边的两点相连

*  存在的问题是不能拖动显示
 *  画出的界面只要重绘之后就清除了

package com.Graphics;
    
    import java.awt.Graphics;
    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.lang.Math;;
    
    public class DrawListener implements MouseListener,MouseMotionListener ,ActionListener {
        
    	private int x1, y1, x2, y2; 
    	private Graphics g;  	// 记录画板上的画布对象
    	private String flag,color;
    	private int san = 0, x10, x20, y10, y20;	// 三角形
    	private int df = 0, dx0, dy0, dx, dy, count = 0;
    	private int line_flag=0,lx=0,ly=0;
    	public DrawListener(Graphics g) {
        
    		this.g = g;
    	}
    	public void actionPerformed(ActionEvent e){
         // 按钮监听
    		//flag = e.getActionCommand();
    		System.out.println(e.getActionCommand());
    		
    		if(e.getActionCommand().equals("三角形")){
        
    			flag="三角形";
    		}else if(e.getActionCommand().equals("多边形")){
        
    			flag="多边形";
    		}else if(e.getActionCommand().equals("直线")){
        
    			flag="直线";
    		}else if(e.getActionCommand().equals("矩形")){
        
    			flag="矩形";
    		}else if(e.getActionCommand().equals("圆")){
        
    			flag="圆";
    		}else if(e.getActionCommand().equals("TEXT")){
        
    			flag="TEXT";
    		}else if(e.getActionCommand().equals("橡皮擦")){
        
    			flag="橡皮擦";
    		}else if(e.getActionCommand().equals("放射直线")){
        
    			flag="放射直线";
    		}		
    		if(e.getActionCommand().equals("green")){
        
    			color="green";
    			
    		}else if(e.getActionCommand().equals("blue")){
        
    			color="blue";
    			
    		}else if(e.getActionCommand().equals("red")){
        
    			color="red";
    			
    		}
    	if(color.equals("green")){
        
    			g.setColor(java.awt.Color.green);
    		}else if(color.equals("blue")){
        		
    			g.setColor(java.awt.Color.blue);
    		}else if(color.equals("red")){
        			
    			g.setColor(java.awt.Color.red);
    		}else
    			g.setColor(java.awt.Color.white);
    	}
    
    	public void mouseDragged(MouseEvent e){
        
    		 int lf=0;
    		 System.out.println("Dragged");
    		 if(flag.equals("橡皮擦")){
        
    			 g.setColor(java.awt.Color.white);
    			 g.fillRect(e.getX(),e.getY(), e.getX()+1, e.getY()+1);
    		 }
    		 else if(flag.equals("直线")&&line_flag==1&&lf==0){
        
    			 g.drawLine(x1, y1, e.getX(), e.getY());
    			 lf=1;
    		 }else if(flag.equals("放射直线")){
        
    			 g.drawLine(x1, y1, e.getX(), e.getY());
    		 }
    		 if(lf==1){
        
    			 lf=0;
    			 java.awt.Color c=g.getColor();
    			 g.setColor(java.awt.Color.white);
    			 g.drawLine(x1, y1,lx,ly);
    			 lx=e.getX();
    			 ly=e.getY();
    			 g.setColor(c);
    		 }
    	 }
        
    	 public void mouseMoved(MouseEvent e){
        		
    		 System.out.println("mouseMoved"); 
    	 }
    
    	// 鼠标按下时点的坐标
    	public void mousePressed(MouseEvent e) {
        
    		// 记录第一次点击的x，y：通过事件e得到
    		x1 = e.getX();
    		y1 = e.getY();
    		System.out.println("按下");
    		if (flag.equals("三角形") && san == 0) {
        
    			x10 = e.getX();
    			y10 = e.getY();
    		} else if (flag.equals("TEXT")) {
        
    			g.drawString("TEXT", x1, y1);
    		} else if (flag.equals("多边形") && df == 0) {
        
    			dx0 = e.getX();
    			dy0 = e.getY();
    			df = 1;
    		}else if(flag.equals("直线")){
        
    			line_flag=1;
    		}
    
    
    	}
    	// 鼠标释放开时点的坐标
    
    	public void mouseReleased(MouseEvent e) {
        
    		// 记录松开的坐标
    		System.out.println("松开");
    		x2 = e.getX();
    		y2 = e.getY();
    		// 得到两次（按下松开）坐标，调用画布对象的方法划线
    	
    		if (flag.equals("三角形") && san == 0) {
        
    			x20 = e.getX();
    			y20 = e.getY();
    			g.drawLine(x10, y10, x20, y20);
    			san = 1;
    		} else if (flag.equals("直线")) {
        
    			g.drawLine(x1, y1, x2, y2);
    			line_flag=0;
    		} else if (flag.equals("矩形")) {
        
    			if (x2 > x1) {
        
    				g.drawRect(x1, y1, Math.abs(x2 - x1), Math.abs(y2 - y1));
    			} else {
        
    				g.drawRect(x2, y2, Math.abs(x2 - x1), Math.abs(y2 - y1));
    			}
    		} else if (flag.equals("圆")) {
        
    			if (x2 > x1) {
        
    				g.drawArc(x1, y1, Math.abs(x2 - x1), Math.abs(y2 - y1), 0, 360);
    			} else {
        
    				g.drawArc(x2, y2, Math.abs(x2 - x1), Math.abs(y2 - y1), 0, 360);
    			}
    		} else if (flag.equals("多边形") && df == 1) {
        
    			df = 2;
    			dx = x2;
    			dy = y2;
    			g.drawLine(x1, y1, x2, y2);
    			System.out.println("("+x1+","+y1+")"+"("+x2+","+y2+")");
    		}
    	}
    
    	public void mouseClicked(MouseEvent e) {
        
    		System.out.println("点击");
    		if (flag.equals("TEXT")) {
        
    			g.drawString("TEXT", x1, y1);
    		} else if (flag.equals("三角形") && san == 1) {
        
    			g.drawLine(x1, y1, x10, y10);
    			g.drawLine(x20, y20, x1, y1);
    			san = 0;
    		} else if (flag.equals("多边形") && df > 0) {
        
    			if (e.getX() == dx && e.getY() == dy && df == 2) {
        // 如果双击
    				count++;
    				if (count == 2) {
        
    					g.drawLine(dx0, dy0, x1, y1);
    					df = 0;
    					System.out.println("("+dx+","+dy+")"+"("+x1+","+y1+")");
    					count = 0;
    				}
    			} else {
        // 单击更新坐标
    				if (df == 2) {
        
    					g.drawLine(x1, y1, dx, dy);
    					System.out.println("("+x1+","+y1+")"+"("+dx+","+dy+")");
    					dx=e.getX();
    					dy=e.getY();
    				}
    			}
    		}
    	}
    
    	public void mouseEntered(MouseEvent e) {
        
    		System.out.println("进入");
    	}
    
    	public void mouseExited(MouseEvent e) {
        
    		System.out.println("退出");
    	}
    }

## 三、优化提升 ##

优化代码、添加按钮图片、重绘  
在自己的win10画图板上截取相关图片，用swing组件添加到窗体的north上。

*  所用到的组件是ImageIcon图标

String[] shape={
        "直线","曲线","矩形","圆","三角形","多边形","放射线","橡皮擦"};
    		for(int i=0;i<shape.length;i++){
        
    			ImageIcon image=new ImageIcon(this.getClass().getResource(shape[i]+".png"));
    			JButton jbu =new JButton(image);//
    			jbu.setActionCommand(shape[i]);//添加字符串
    			jbu.setPreferredSize(new Dimension(25, 25));
    			northPlane.add(jbu);
    			jbu.addActionListener(mouse);
    		}

*  重绘原理：把监听器监听到的所有鼠标动作（画出来的线），记录下来，当窗体重绘的时候再次显示。定义一个repaint类，包含画图方式name，颜色，按下放开两点（三角形三个点），我们用一个很大的数组来保存每一次画图记录
 *  每个组件都有对应的paint方法，可以直接继承JFrame窗体类，重写paint方法

public void paint(Graphics g){
        
    		//g=jf.();
    		super.paint(g);
    		//取出数组中的图形对象
    		for(int i=0;i<repaint.length;i++){
        
    			Repaint rp=repaint[i];
    			if(rp!=null){
        
    				rp.Drawpaint(g);
    			}else break;
    		}
    	}

package com.Graphics02;
    
    import java.awt.Color;
    import java.awt.Graphics;
    
    //图形类
    public class Repaint {
        
    	private int x1,y1,x2,y2,x3,y3;
    	private String name;
    	private Color c;
    	public Repaint(String name,Color c,int x1,int y1,int x2,int y2){
        
    		this.name=name;
    		this.x1=x1;
    		this.x2=x2;
    		this.y1=y1;
    		this.y2=y2;
    		this.c=c;
    	}
    	public void setsan(int x,int y){
        
    		this.x3=x;
    		this.y3=y;
    	}
    	public void Drawpaint(Graphics g){
        
    		g.setColor(c);
    		switch (name){
        
    		case "直线":
    			g.drawLine(x1, y1, x2, y2);
    			break;
    		case "多边形":
    			g.drawLine(x1, y1, x2, y2);
    			break;
    		case "矩形":
    			g.drawRect(Math.min(x2, x1), Math.min(y1, y2), Math.abs(x1-x2), Math.abs(y1-y2));
    			break;
    		case "圆":
    			g.drawArc(Math.min(x1, x2), Math.min(y2, y1), Math.abs(x1 - x2), Math.abs(y1 - y2), 0, 360);
    			break;
    		case "三角形":
    			g.drawLine(x1, y1, x2, y2);
    			g.drawLine(x1, y1, x3, y3);
    			g.drawLine(x3, y3, x2, y2);
    			break;
    		case "橡皮擦":
    			g.clearRect(x1, y1, x2, y2);;
    			break;
    		case "曲线":
    			g.drawLine(x1, y1, x2, y2);
    			break;
    		}
    	}
    }

有了重绘功能就可以实现拖动了，在我们电脑里面的画图板都是在画图的时候可以拖动看见线条的，可以用重绘来实现，在监听器中再继承一个`MouseMotionListener`可监听鼠标移动，拖动

*  在鼠标拖动方法里面添加不断划线，要用白线覆盖原来画出来的线，再画一个新的线
 *  拖动时的线条覆盖问题：每次在要划线前面添加重绘

public void mouseDragged(MouseEvent e) {
        // 拖动
    		//g.setColor(color);
    		if(shape != null){
        
    		for(int i=0;i<shape.length;i++){
        
    			Repaint rp=shape[i];
    			if(rp!=null){
        
    				rp.Drawpaint(g);
    			}else break;
    		}
    		}
    		//Color c = g.getColor();
    		if (name.equals("直线") || name.equals("三角形")) {
        
    			g.setColor(Color.white);
    			g.drawLine(x1, y1, x3, y3);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawLine(x1, y1, x3, y3);
    		} else if (name.equals("矩形")) {
        
    			g.setColor(Color.white);
    			g.drawRect(Math.min(x1, x3), Math.min(y1, y3), Math.abs(x1 - x3), Math.abs(y1 - y3));
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawRect(Math.min(x1, x3), Math.min(y1, y3), Math.abs(x1 - x3), Math.abs(y1 - y3));
    		}else if (name.equals("圆")){
        
    			g.setColor(Color.white);
    			g.drawArc(Math.min(x1, x3), Math.min(y3, y1), Math.abs(x1 - x3), Math.abs(y1 - y3), 0, 360);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawArc(Math.min(x1, x3), Math.min(y3, y1), Math.abs(x1 - x3), Math.abs(y1 - y3), 0, 360);
    			
    		}
    		else if (name.equals("橡皮擦")) {
        
    			// Color c=g.getColor();
    			g.setColor(Color.white);
    		//	g.clearRect(e.getX(), e.getY(), e.getX() + 1, e.getY() + 1);
    			Repaint rp=new Repaint(name,g.getColor(),e.getX(),e.getY(),1,1);
    			shape[index++]=rp;
    			g.setColor(color);
    		} else if (name.equals("曲线")) {
        
    			g.setColor(color);
    			g.drawLine(e.getX(), e.getY(), x1, y1);
    			Repaint rp=new Repaint(name,g.getColor(),e.getX(),e.getY(),x1,y1);
    			shape[index++]=rp;
    			// g.drawLine(x1, y1, x3, y3);
    			x1 = e.getX();
    			y1 = e.getY();
    
    		}
    
    	}

*  在电脑的画图板里面，多边形没有拖动显示，只要点击了一个点就有连接到，可以在鼠标移动的方法里面添加多边形的绘制

public void mouseMoved(MouseEvent e) {
        // 移动
    		
    		if(shape != null){
        
    		for(int i=0;i<shape.length;i++){
        
    			Repaint rp=shape[i];
    			if(rp!=null){
        
    				rp.Drawpaint(g);
    			}else break;
    		}
    	}
    		Color c = g.getColor();
    		if (name.equals("多边形") && duo_flag == 1) {
        
    			g.setColor(Color.white);
    			g.drawLine(dx, dy, x3, y3);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(c);
    			g.drawLine(dx, dy, x3, y3);
    		}
    	
    	}

效果图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODA0MzYz_size_16_color_FFFFFF_t_70]

## 四、最终版本 ##

在上一次的基础加入可选择线条粗细的功能，不过貌似效果不是很好，再次选择粗细的时候画曲线会卡顿。  
可选择画笔粗细的是Graphics2D类，在上一个份代码中修改Graphic类就可以了，添加可选择粗细的按钮，方法同上，要注意的是重绘方法依旧是获取画笔Graphic这个类的画笔，这里需要强制转型：

public void paint(Graphics g){
        
    		Graphics2D g0=(Graphics2D)g;
    		super.paint(g);
    		//取出数组中的图形对象
    		System.out.println("重绘函数");
    		for(int i=0;i<repaint.length;i++){
        
    			Repaint rp=repaint[i];
    			if(rp!=null){
        
    				rp.Drawpaint(g0);
    			}else break;
    		}
    		
    	}

*  为了让我们画出来的线不能越界（画到按钮上），使用边框布局，所以我们在窗体类中应该要继承JPanel获取center的画笔，重绘center
 *  show

package com.Graphics03;
    
    import java.awt.BorderLayout;
    import java.awt.Color;
    import java.awt.Dimension;
    import java.awt.Graphics;
    import java.awt.Graphics2D;
    
    import javax.swing.ImageIcon;
    import javax.swing.JButton;
    import javax.swing.JFrame;
    import javax.swing.JPanel;
    
    public class Draw extends JPanel{
        
    	private Repaint[] repaint=new Repaint[100000];//重绘对象数组
    //	Graphics g;
    //	private Graphics2D g=(Graphics2D) this.getGraphics();
    	
    	public static void main(String [] args){
        
    		Draw draw=new Draw();
    		draw.showUI();
    	}
    	
    	public void showUI(){
        
    		//创建窗体对象
    		JFrame jf=new JFrame(); //改成this 子类
    		jf.setSize(800, 600);
    		jf.setTitle("画板界面");
    		//设置退出进程方法
    		jf.setDefaultCloseOperation(3);
    		//设置居中
    		jf.setLocationRelativeTo(null);
    		//设置背景色
    		jf.getContentPane().setBackground(Color.white);
    		jf.setLayout(new BorderLayout());//设置边框布局
    		//三
    		JPanel northPlane = new JPanel();  //容器
    		northPlane.setBackground(Color.white); //
    		northPlane.setPreferredSize(new Dimension(0, 40));
    		jf.add(northPlane,BorderLayout.NORTH);
    		
    	//	JPanel centerPlane = new JPanel();
    		this.setBackground(Color.WHITE);
    		jf.add(this,BorderLayout.CENTER);
    		//san
    		
    		DrawMouse mouse=new DrawMouse(this);//新建鼠标监听器
    		//事件监听器
    				//1.事件源：当前动作所发生的组件
    				//2.确定监听器方法：鼠标监听器方法
    				//3.绑定事件处理类
    		String[] shape={
        "直线","曲线","矩形","圆","三角形","多边形","放射线","橡皮擦","1","2","3"};
    		for(int i=0;i<shape.length;i++){
        
    			ImageIcon image=new ImageIcon(this.getClass().getResource(shape[i]+".png"));
    			JButton jbu =new JButton(image);
    			jbu.setActionCommand(shape[i]);//添加字符串
    			jbu.setPreferredSize(new Dimension(25, 25));
    			northPlane.add(jbu);
    			jbu.addActionListener(mouse);
    		}
    		Color[] color={
        Color.BLUE,Color.red,Color.green};
    		for(int i=0;i<color.length;i++){
        
    			JButton jbu =new JButton();
    			jbu.setBackground(color[i]);
    			jbu.setPreferredSize(new Dimension(30,30));
    			northPlane.add(jbu);
    			jbu.addActionListener(mouse);
    		}
    		jf.setVisible(true);
    		
    	//	mouse.setgra(g);
    		mouse.setRepaint(repaint);
    		this.addMouseListener(mouse);//鼠标监听方法
    		this.addMouseMotionListener(mouse);//鼠标拖动事件
    	
    		
    		
    	}
    	/**
    	 * 重写绘制组件的方法
    	 */
    	public void paint(Graphics g){
        
    		
    		Graphics2D g0=(Graphics2D)g;
    		super.paint(g);
    		//取出数组中的图形对象
    		System.out.println("重绘函数");
    		for(int i=0;i<repaint.length;i++){
        
    			Repaint rp=repaint[i];
    			if(rp!=null){
        
    				rp.Drawpaint(g0);
    			}else break;
    		}
    		
    	}
    }

监听器：

package com.Graphics03;
    
    import java.awt.BasicStroke;
    import java.awt.Color;
    import java.awt.Graphics;
    import java.awt.Graphics2D;
    import java.awt.Shape;
    import java.awt.Stroke;
    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 javax.swing.JButton;
    //import javax.swing.JPanel;
    
    public class DrawMouse implements MouseListener, ActionListener, MouseMotionListener {
        
    	Color color = Color.BLACK;
    	private int x1, y1, x2, y2, x3, y3, sx0, sy0, sx, sy, dx, dy, dx0, dy0;
    	private int san_flag = 0, duo_flag = 0;
    	private float wi = 1;
    	private String name = "直线";
    	private Repaint[] shape;
    	private int index = 0;
    	private Draw draw;
    	private Graphics2D g;// 保存传递的画笔
    
    	public DrawMouse(Draw draw) {
        
    		this.draw = draw;
    
    	}
    
    	public void setRepaint(Repaint[] shape) {
        
    		this.shape = shape;
    	}
    
    	public void actionPerformed(ActionEvent e) {
        // 按键监听器
    		// g=draw.getGraphics();
    		if (e.getActionCommand().equals("")) {
        
    			JButton jbu = (JButton) e.getSource();// 获取当前事件源
    			color = jbu.getBackground();
    			g.setColor(color);
    			// System.out.println(color);
    		} else if (e.getActionCommand().equals("1")) {
        
    			wi = 1.0f;
    		} else if (e.getActionCommand().equals("2")) {
        
    			wi = 2.0f;
    		} else if (e.getActionCommand().equals("3")) {
        
    			wi = 3.0f;
    		} else {
        
    			name = e.getActionCommand();
    		}
    	}
    
    	public void mouseClicked(MouseEvent e) {
        // 点击
    
    		// g=draw.getGraphics();
    		if (name.equals("三角形") && san_flag == 1) {
        
    			g.drawLine(e.getX(), e.getY(), sx0, sy0);
    			g.drawLine(e.getX(), e.getY(), sx, sy);
    			Repaint rp = new Repaint(name, g.getColor(), wi, sx0, sy0, sx, sy);
    			rp.setsan(e.getX(), e.getY());
    			shape[index++] = rp;
    			san_flag = 0;
    		} else if (name.equals("多边形") && duo_flag == 1) {
        
    			g.drawLine(x1, y1, dx, dy);
    			Repaint rp = new Repaint(name, g.getColor(), wi, x1, y1, dx, dy);
    			shape[index++] = rp;
    			if (dx == e.getX() && dy == e.getY()) {
        
    				g.drawLine(dx0, dy0, x1, y1);
    				Repaint rp0 = new Repaint(name, g.getColor(), wi, x1, y1, dx0, dy0);
    				shape[index++] = rp0;
    				duo_flag = 0;
    			} else {
        
    				dx = e.getX();
    				dy = e.getY();
    			}
    		}
    	}
    
    	public void mousePressed(MouseEvent e) {
        // 按下
    		// g = draw.getGraphics();
    		g.setColor(color);
    		x1 = e.getX();
    		y1 = e.getY();
    		System.out.println(x1 + " " + y1);
    
    	}
    
    	public void mouseReleased(MouseEvent e) {
        // 放开
    		// g=draw.getGraphics();
    		x2 = e.getX();
    		y2 = e.getY();
    		// g.setColor(color);
    		System.out.println(g.getColor());
    		System.out.println(x2 + " " + y2);
    
    		if (name.equals("直线")) {
        
    			g.drawLine(x1, y1, x2, y2);
    			Repaint rp = new Repaint(name, g.getColor(), wi, x1, y1, x2, y2);
    			shape[index++] = rp;
    		} else if (name.equals("矩形")) {
        
    			g.drawRect(Math.min(x1, x2), Math.min(y1, y2), Math.abs(x1 - x2), Math.abs(y1 - y2));
    			Repaint rp = new Repaint(name, g.getColor(), wi, x1, y1, x2, y2);
    			shape[index++] = rp;
    		} else if (name.equals("圆")) {
        
    			g.drawArc(Math.min(x1, x2), Math.min(y2, y1), Math.abs(x1 - x2), Math.abs(y1 - y2), 0, 360);
    			Repaint rp = new Repaint(name, g.getColor(), wi, x1, y1, x2, y2);
    			shape[index++] = rp;
    		} else if (name.equals("三角形") && san_flag == 0) {
        
    			san_flag = 1;
    			g.drawLine(x1, y1, x2, y2);
    			sx0 = x1;
    			sy0 = y1;
    			sx = x2;
    			sy = y2;
    
    		} else if (name.equals("多边形") && duo_flag == 0) {
        
    			duo_flag = 1;
    			g.drawLine(x1, y1, x2, y2);
    			Repaint rp = new Repaint(name, g.getColor(), wi, x1, y1, x2, y2);
    			shape[index++] = rp;
    			dx0 = x1;
    			dy0 = y1;
    			dx = x2;
    			dy = y2;
    		}
    	}
    
    	public void mouseEntered(MouseEvent e) {
        // 进入
    		g = (Graphics2D) draw.getGraphics();
    		g.setStroke(new BasicStroke(wi));
    
    	}
    
    	public void mouseExited(MouseEvent e) {
        // 退出
    	}
    
    	public void mouseDragged(MouseEvent e) {
        // 拖动
    		// g.setColor(color);
    		if (shape != null && (!name.equals("橡皮擦"))) {
        
    			for (int i = 0; i < shape.length; i++) {
        
    				Repaint rp = shape[i];
    				if (rp != null) {
        
    					rp.Drawpaint(g);
    				} else
    					break;
    			}
    		}
    		// Color c = g.getColor();
    		if (name.equals("直线") || name.equals("三角形")) {
        
    			g.setColor(Color.white);
    			g.drawLine(x1, y1, x3, y3);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawLine(x1, y1, x3, y3);
    		} else if (name.equals("矩形")) {
        
    			g.setColor(Color.white);
    			g.drawRect(Math.min(x1, x3), Math.min(y1, y3), Math.abs(x1 - x3), Math.abs(y1 - y3));
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawRect(Math.min(x1, x3), Math.min(y1, y3), Math.abs(x1 - x3), Math.abs(y1 - y3));
    		} else if (name.equals("圆")) {
        
    			g.setColor(Color.white);
    			g.drawArc(Math.min(x1, x3), Math.min(y3, y1), Math.abs(x1 - x3), Math.abs(y1 - y3), 0, 360);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(color);
    			g.drawArc(Math.min(x1, x3), Math.min(y3, y1), Math.abs(x1 - x3), Math.abs(y1 - y3), 0, 360);
    
    		} else if (name.equals("橡皮擦")) {
        
    			// Color c=g.getColor();
    			g.setColor(Color.white);
    			g.drawLine(e.getX(), e.getY(), x1, y1);
    			Repaint rp = new Repaint(name, g.getColor(), wi, e.getX(), e.getY(), x1, y1);
    			shape[index++] = rp;
    			// g.drawLine(x1, y1, x3, y3);
    			x1 = e.getX();
    			y1 = e.getY();
    		} else if (name.equals("曲线")) {
        
    			g.setColor(color);
    			g.drawLine(e.getX(), e.getY(), x1, y1);
    			Repaint rp = new Repaint(name, g.getColor(), wi, e.getX(), e.getY(), x1, y1);
    			shape[index++] = rp;
    			// g.drawLine(x1, y1, x3, y3);
    			x1 = e.getX();
    			y1 = e.getY();
    
    		}
    
    	}
    
    	public void mouseMoved(MouseEvent e) {
        // 移动
    
    		if (shape != null && name.equals("多边形")) {
        
    			for (int i = 0; i < shape.length; i++) {
        
    				Repaint rp = shape[i];
    				if (rp != null) {
        
    					rp.Drawpaint(g);
    				} else
    					break;
    			}
    		}
    		Color c = g.getColor();
    		if (name.equals("多边形") && duo_flag == 1) {
        
    			g.setColor(Color.white);
    			g.drawLine(dx, dy, x3, y3);
    			x3 = e.getX();
    			y3 = e.getY();
    			g.setColor(c);
    			g.drawLine(dx, dy, x3, y3);
    		}
    
    	}
    }

最终效果  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODA0MzYz_size_16_color_FFFFFF_t_70 1]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODA0MzYz_size_16_color_FFFFFF_t_70]: /images/20220323/eb219ae9688745b5810084de8a8ee5e8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3FxXzM2ODA0MzYz_size_16_color_FFFFFF_t_70 1]: /images/20220323/33d16085445345c9985e30d20882bd3c.png