绘图器（java）

按住鼠标左键可以完成绘图，鼠标右键可以完成颜色的切换。

import java.awt.*;
import java.awt.event.*;
import java.awt.image.BufferedImage;

public class HandDraw {
    //定义窗口对象
    private frame frame=new frame("简单手绘程序");

    //定义画图区的宽高
    private final int AREA_WIDTH=500;
    private final int AREA_HEIGHT=400;

    //定义一个右键菜单，用于设置画笔的颜色
    private PopupMenu colorMenu=new PopupMenu();
    private MenuItem readItem=new MenuItem("红色");
    private MenuItem greenItem=new MenuItem("绿色");
    private MenuItem blueItem=new MenuItem("蓝色");

    //定义一个变量，记录当前画笔的颜色
    private Color forceColor=Color.BLACK;

    //定义变量，记录鼠标拖动过程中，上一次所处的坐标
    private int preX=-1;
    private int preY=-1;

    //创建一个BufferedImage位图对象
    BufferedImage image=new BufferedImage(AREA_WIDTH,AREA_HEIGHT,BufferedImage.TYPE_INT_RGB);

    //通过位图来获取关联的Graphics对象
    Graphics g=image.getGraphics();

    //定义一个类继承Canvas
    private class MyCanvas extends Canvas{
        @Override
        public void paint(Graphics g) {
            g.drawImage(image,0,0,null);
        }
    }

    MyCanvas drawArea=new MyCanvas();


    public void init(){
        //组装视图

        ActionListener listener=new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                String actionCommand = e.getActionCommand();
                switch (actionCommand){
                    case "红色":
                        forceColor= Color.RED;
                        break;
                    case "绿色":
                        forceColor=Color.GREEN;
                        break;
                    case"蓝色":
                        forceColor=Color.BLUE;
                        break;
                }
            }
        };

        readItem.addActionListener(listener);
        greenItem.addActionListener(listener);
        blueItem.addActionListener(listener);

        colorMenu.add(readItem);
        colorMenu.add(blueItem);
        colorMenu.add(greenItem);

        //把colorMenu设置给绘图区域
        drawArea.add(colorMenu);

        drawArea.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseReleased(MouseEvent e) {//当鼠标键抬起时被调用
                boolean popupTrigger = e.isPopupTrigger();
                if(popupTrigger){
                    colorMenu.show(drawArea,e.getX(),e.getY());
                }

                //重置preX, preY
                preX=-1;
                preY=-1;
            }
        });

        //设置位图背景为白色
        g.setColor(Color.white);
        g.fillRect(0,0,AREA_WIDTH,AREA_HEIGHT);

        //通过监听鼠标的移动，完成线条绘制
        drawArea.addMouseMotionListener(new MouseMotionAdapter() {
            //该方法，当鼠标左键按下，并拖动时，会被调用
            @Override
            public void mouseDragged(MouseEvent e) {
                if(preX>0&&preY>0) {
                    g.setColor(forceColor);
                    //画线条,需要两组坐标，分别代表线条的起点和终点，e.getX(),e.getY()可以获得终点的坐标
                    g.drawLine(preX, preY, e.getX(), e.getY());
                }

                //修正preX, preY的值
                preX=e.getX();
                preY=e.getY();

                //重绘组件
                drawArea.repaint();
            }
        });
        drawArea.setPreferredSize(new Dimension(AREA_WIDTH,AREA_HEIGHT));
        frame.add(drawArea);

        frame.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        //设置frame最佳大小并可见
        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        HandDraw hd=new HandDraw();
        hd.init();
    }
}