Java简单图形编辑器 放置、移动和擦除方块 鼠标事件测试程序 Java核心技术 事件处理

package com.sunnyykn.chapter08;

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

/**
*
* A panel with mouse operations for adding and removing squares.
* @author sunnyykn
*
*/
class MousePanel extends JPanel
{
private static final int SIDELENGTH = 10;
private ArrayList<Rectangle2D> squares;
private Rectangle2D current;
//the square containing the mouse cursor

public MousePanel()
{
squares = new ArrayList<Rectangle2D>();
current = null;

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

public void paintComponent(Graphics g)
{
super.paintComponent(g);
Graphics2D g2 = (Graphics2D) g;

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

/**
* Finds the first square containing a point
* @param p a point
* @return the first square that contains p
* @author sunnyykn
*
*/
public Rectangle2D find(Point2D p)
{
for (Rectangle2D r : squares)
{
if (r.contains(p)) return r;
}
return null;
}

/**
* Add a square to the collection
* @param p the centre of the square
* @author sunnyykn
*
*/
public void add(Point2D p)
{
double x = p.getX();
double y = p.getY();

current = new Rectangle2D.Double(
x - SIDELENGTH / 2,
y - SIDELENGTH / 2,
SIDELENGTH,
SIDELENGTH);
squares.add(current);
repaint();
}

/**
* Removes a square from the collection
* @param s the square to remove
* @author sunnyykn
*
*/
public void remove(Rectangle2D s)
{
if (s == null) return;
if (s == current) current = null;
squares.remove(s);
repaint();
}

private class MouseHandler extends MouseAdapter
{
public void mousePressed(MouseEvent event)
{
// add a new square if the cursor isn't inside a square
current = find(event.getPoint());
if (current == null)
add(event.getPoint());
}

public void mouseClicked(MouseEvent event)
{
//remove the current square if double clicked
current = find(event.getPoint());
if (current != null && event.getClickCount() >= 2)
remove(current);
}
}

private class MouseMotionHandler implements MouseMotionListener
{
public void mouseMoved(MouseEvent event)
{
//set the mouse cursor to cross hairs if it is inside
//a rectangle

if (find(event.getPoint()) == null)
setCursor(Cursor.getDefaultCursor());
else
setCursor(Cursor.getPredefinedCursor(Cursor.CROSSHAIR_CURSOR));
}

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

//drag the current rectangle to center it at (x,y)
current.setFrame(
x - SIDELENGTH / 2,
y - SIDELENGTH / 2,
SIDELENGTH,
SIDELENGTH);
repaint();
}
}
}
}

/**
* A frame containing a panel for testing mouse operations
* @author sunnyykn
*
*/
class MouseFrame extends JFrame
{
public static final int DEFAULT_WIDTH = 300;
public static final int DEFAULT_HEIGHT = 200;

public MouseFrame()
{
setTitle("MouseTest Sunnyykn");
setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);

//add panel to frame

MousePanel panel = new MousePanel();
add(panel);
}
}

public class MouseTest {
public static void main(String args[])
{
MouseFrame frame = new MouseFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setVisible(true);
}
}