Java事件处理

创建一个可以通过鼠标按钮选择FrameBackground的背景颜色。

package button;

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


public class ButtonFrame extends JFrame 
{
	private JPanel buttonPanel;
	private static final int DEFAULT_WIDTH = 300;
	private static final int DEFAULT_HEIGHT = 200;
	
	public ButtonFrame()
	{
		setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
		
		JButton yellowButton = new JButton("Yellow");
		JButton blueButton = new JButton("Blue");
		JButton redButton = new JButton("Red");
		
		buttonPanel = new JPanel();
		
		buttonPanel.add(yellowButton);
		buttonPanel.add(blueButton);
		buttonPanel.add(redButton);
		
		add(buttonPanel);
		
		ColorAction yellowAction = new ColorAction(Color.YELLOW);
		ColorAction blueAction = new ColorAction(Color.BLUE);
		ColorAction redAction = new ColorAction(Color.RED);
		
		yellowButton.addActionListener(yellowAction);
		blueButton.addActionListener(blueAction);
		redButton.addActionListener(redAction);
	}
	
	private class ColorAction implements ActionListener
	{
		private Color backgroundColor;
		
		public ColorAction(Color c)
		{
			backgroundColor = c;
		}
		
		public void actionPerformed(ActionEvent event)
		{
			buttonPanel.setBackground(backgroundColor);
		}
	}
}

可以更改观感。

package plaf;

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

public class PlafFrame extends JFrame
{
	private static final int DEFAULT_WIDTH = 500;
	private static final int DEFAULT_HEIGHT = 400;
	private JPanel buttonPanel;
	
	public PlafFrame()
	{
		setSize(DEFAULT_WIDTH,DEFAULT_HEIGHT);
		
		buttonPanel = new JPanel();
		
		UIManager.LookAndFeelInfo[] infos = UIManager.getInstalledLookAndFeels();
		
		for (UIManager.LookAndFeelInfo info : infos)
			makeButton(info.getName(),info.getClassName());
		
		add(buttonPanel);
		pack();
	}
	
	void makeButton(String name,final String plafName)
	{
		JButton button = new JButton(name);
		buttonPanel.add(button);
		
		button.addActionListener(new ActionListener(){
			
			public void actionPerformed(ActionEvent event)
			{
				try
				{
					UIManager.setLookAndFeel(plafName);
					SwingUtilities.updateComponentTreeUI(PlafFrame.this);
					pack();
				}
				catch (Exception e)
				{
					e.printStackTrace();
				}
			}
			
		});
	}
}

可以通过键盘改变颜色。

package action;

import java.awt.*;
import java.awt.event.*;

import javax.swing.*;

public class ActionFrame extends JFrame
{
	private JPanel buttonPanel;
	private static final int DEFAULT_WIDTH = 1000;
	private static final int DEFAULT_HEIGHT = 200;
	
	public ActionFrame()
	{
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
		buttonPanel = new JPanel();
		
		Action yellowAction = new ColorAction("Yellow",new ImageIcon("yellow-ball.gif"),Color.yellow);
		Action blueAction = new ColorAction("Blue",new ImageIcon("blue-ball.gif"),Color.blue);
		Action redAction = new ColorAction("Red",new ImageIcon("red-ball.gif"),Color.red);
		
		buttonPanel.add(new JButton(yellowAction));
		buttonPanel.add(new JButton(blueAction));
		buttonPanel.add(new JButton(redAction));
		
		add(buttonPanel);
		
		InputMap imap = buttonPanel.getInputMap(JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT);
		imap.put(KeyStroke.getKeyStroke("ctrl Y"), "panel.yellow");
		imap.put(KeyStroke.getKeyStroke("ctrl B"), "panel.blue");
		imap.put(KeyStroke.getKeyStroke("ctrl R"), "panel.red");
		
		ActionMap amap = buttonPanel.getActionMap();
		amap.put("panel.yellow",yellowAction);
		amap.put("panel.blue", blueAction);
		amap.put("panel.red", redAction);
	}
	
	public class ColorAction extends AbstractAction
	{
		public ColorAction(String name,Icon icon,Color c)
		{
			putValue(Action.NAME,name);
			putValue(Action.SMALL_ICON,icon);
			putValue(Action.SHORT_DESCRIPTION,"Set panel color to "+ name.toLowerCase());
			putValue("color",c);
		}
		
		public void actionPerformed(ActionEvent event)
		{
			Color c = (Color) getValue("color");
			buttonPanel.setBackground(c);
		}
	}
}

可以通过鼠标点击创建方块，双击消除方块，拖动方块，十字鼠标图案。

package mouse;

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

public class MouseComponent extends JComponent
{
	private static final int SIDELENGTH = 10;
	private ArrayList<Rectangle2D> squares;
	private Rectangle2D current;
	
	public MouseComponent()
	{
		squares = new ArrayList<>();
		current = null;
		
		addMouseListener(new MouseHandler());
		addMouseMotionListener(new MouseMotionHandler());
	}
	
	public void paintComponent(Graphics g)
	{
		Graphics2D g2 = (Graphics2D) g;
		for (Rectangle2D r : squares)
			g2.draw(r);
	}
	
	public Rectangle2D find(Point2D p)
	{
		for (Rectangle2D r : squares)
		{
			if (r.contains(p)) return r;
		}
		return null;
	}

	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();
	}

	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)
		{
			current = find(event.getPoint());
			if (current == null) add(event.getPoint());
		}
	
		public void mouseClicked(MouseEvent event)
		{
			current = find(event.getPoint());
			if (current != null && event.getClickCount() >=2) remove(current); 
		}
	}
	
	private class MouseMotionHandler implements MouseMotionListener
	{
		public void mouseMoved(MouseEvent event)
		{
			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();
				
				current.setFrame(x-SIDELENGTH/2,y-SIDELENGTH/2,SIDELENGTH,SIDELENGTH);
				repaint();
			}
		}
	}	
}