Java 写字板

Java 写字板

源代码：

文件：WriteBoard.java

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;
import java.awt.Graphics;
import java.awt.MenuItem;
import java.awt.PopupMenu;
import java.awt.event.ActionListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionAdapter;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.image.BufferedImage;

import javax.swing.JPanel;

public class WriteBoard {
    private int X;
    private int Y;
    private final int WIDTH = 800;
    private final int HEIGHT = 500;
    private Frame frame;
    private BufferedImage image;
    private Graphics graphics;
    private Color curColor;
    private PopupMenu menu;
    private MenuItem item;
    private JPanel canvas = new JPanel() {
        @Override
        public void paint(Graphics g) {
            g.drawImage(image, 0, 0, null);
        }
    };
    private ActionListener action = e->{
        if (e.getActionCommand().equals("蓝色")) {
            curColor = new Color(0, 0, 255);
            graphics.setColor(curColor);
        }
        if (e.getActionCommand().equals("红色")) {
            curColor = new Color(255, 0, 0);
            graphics.setColor(curColor);
        }
        if (e.getActionCommand().equals("绿色")) {
            curColor = new Color(0, 255, 0);
            graphics.setColor(curColor);
        }
        if (e.getActionCommand().equals("黄色")) {
            curColor = new Color(255, 242, 0);
            graphics.setColor(curColor);
        }
        if (e.getActionCommand().equals("青色")) {
            curColor = new Color(153, 217, 214);
            graphics.setColor(curColor);
        }
    };

    private WriteBoard() {
        X = -1;
        Y = -1;
        image = new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_BGR);
        frame = new Frame("写字板");
        curColor = new Color(0, 0, 0);
        graphics = image.getGraphics();
        menu = new PopupMenu();
        item = new MenuItem("蓝色");
        item.addActionListener(action);
        menu.add(item);
        item = new MenuItem("红色");
        item.addActionListener(action);
        menu.add(item);
        item = new MenuItem("绿色");
        item.addActionListener(action);
        menu.add(item);
        item = new MenuItem("黄色");
        item.addActionListener(action);
        menu.add(item);
        item = new MenuItem("青色");
        item.addActionListener(action);
        menu.add(item);
        canvas.add(menu);
    }

    public void draw() {
        frame.add(canvas);
        frame.addWindowListener(new WindowAdapter() {
            public void windowClosing(WindowEvent e) {
                System.exit(0);
            }
        });
        canvas.addMouseMotionListener(new MouseMotionAdapter() {

            @Override
            public void mouseDragged(MouseEvent e) {
                if (X >= 0 && Y >= 0) {
                    graphics.drawLine(X, Y, e.getX(), e.getY());
                }
                X = e.getX();
                Y = e.getY();
                canvas.repaint();
            }

        });
        canvas.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseReleased(MouseEvent e) {
                if (e.isPopupTrigger()) {
                    menu.show(canvas, e.getX(), e.getY());
                }
                X = -1;
                Y = -1;
            }
        });
        canvas.setPreferredSize(new Dimension(WIDTH, HEIGHT));
        graphics.fillRect(0, 0, WIDTH, HEIGHT);
        graphics.setColor(curColor);
        frame.pack();
        frame.setVisible(true);
    }

    public static void getWriteBoard() {
        new WriteBoard().draw();
    }

}

文件：Test.java

public class Test {
    public static void main(String[] args) {
        WriteBoard.getWriteBoard();
    }
}