鼠标点击事件处理

程序概述

在示例中，提供了 mousePressed 和 mouseClicked 方法。当鼠标点击在所有小方块的像素之外时，就会绘制一个新的小方块。这个操作在 mousePressed 方法中实现的，这样可以让用户的操作立即得到相应，而不必等到释放鼠标按键。如果用户在某个小方块中双击鼠标，就会将它擦除。由于需要知道点击的次数，这个操作在mouseClick中实现。

mouse/MouseFrame.java

程序的主类

package mouse;

import javax.swing.*;

public class MouseFrame extends JFrame{
    private static final long serialVersionUID = 1L;
    public static void main(String[] args){
        MouseFrame mouseFrame = new MouseFrame();
        mouseFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        mouseFrame.setVisible(true);
    }

    public MouseFrame() {
        add(new MouseComponent());
        pack();
    }
}

mouse/MouseComponent.java

package mouse;

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import javax.swing.*;

public class MouseComponent extends JComponent{
    private static final long serialVersionUID = 1L;

    private static final int SIZELENGTH = 10;  //小方块的边长
    private ArrayList<Rectangle2D> squares;   // 存储小方块的坐标的动态数组，数组中每个元素是一个矩形对象
    private Rectangle2D current;    //当前小方块

    public MouseComponent(){
        squares = new ArrayList<>(); 
        current = null;

        addMouseListener(new MouseHandler());
        addMouseMotionListener(new MouseMotionHandler());
    }

    //画小方块
    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D) g;

        for (Rectangle2D r : squares)
            g2.draw(r);
    }

    //寻找并返回鼠标指向的第一个小方块
    public Rectangle2D find(Point2D p) {    
        for (Rectangle2D r : squares)
            if (r.contains(p)) return r;
        return null;
    }

    //在此时鼠标所指的地方增加小方块
    public void add(Point2D p) {
        double x = p.getX();
        double y = p.getY();

        //以鼠标点击点为中心画正方形
        current = new Rectangle2D.Double(x - SIZELENGTH / 2, y - SIZELENGTH / 2, SIZELENGTH, SIZELENGTH);
        squares.add(current);
        repaint();
    }

    //移除小方块
    public void remove(Rectangle2D s){
        if (s == null) return;
        if (s == current) current = null;
        squares.remove(s);
        repaint();
    }

    /**
     * 鼠标点击事件类
     */
    private class MouseHandler extends MouseAdapter {
        //点击鼠标立即创建一个小方块，而不必等到释放鼠标按键
        public void mousePressed(MouseEvent event){
            current = find(event.getPoint());
            if (current == null) add(event.getPoint());
        }
        
        //点击鼠标并释放，需要统计点击的次数，用来判断是否移除方块
        public void mouseClicked(MouseEvent event){
            current = find(event.getPoint());
            if (current != null && event.getClickCount() >=2) remove(current);
        }
    }

    /**
     * 鼠标移动事件接口
     */
    public class MouseMotionHandler implements MouseMotionListener{
        
        public void mouseMoved(MouseEvent event){
            if (find(event.getPoint()) == null)    //鼠标没有指到小方块
                setCursor(Cursor.getDefaultCursor());       //默认形状
            else        //鼠标指到小方块
                setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));    //鼠标变成十字形
        }

        public void mouseDragged(MouseEvent event){
            if (current != null){
                int x = event.getX();
                int y = event.getY();

                current.setFrame(x - SIZELENGTH / 2, y - SIZELENGTH / 2, SIZELENGTH, SIZELENGTH);
                repaint();
            }
        }
    }
    
    //返回一个窗口的大小用于程序的首选窗口
    private static final int DEFAULT_WIDTH = 700;
    private static final int DEFAULT_HEIGHT = 500;
    
    public Dimension getPreferredSize() {
        return new Dimension(DEFAULT_WIDTH, DEFAULT_HEIGHT);
    }
}

• 学习《Java核心技术卷一》之事件处理