Java事件初步

GUI程序发展到现在，事件一直是其核心。
从以前的Win32程序，处理事件需要编写代码来检查事件队列，代码由switch来控制，这种方式编写的程序可读性很差。
后来的Visual Basic，.NET，将事件对程序员隐藏起来。

那么，我们Java中是如何处理事件的呢？
Java对事件控制作了综合，实现了从事件源到事件监听器的传递。

事件源注册事件监听器对象，如下：
eventSourceObject.addEventListener(eventListenerObject);


eg:
ActionListener listener = ...;
JButton button = new JButton("Ok");
button.addActionListener(listener);


下面我们来举个例子，我们做个Frame,在上面放个面板(Panel)，在Panel上再放个
button，点击button，弹出对话框。
这是一个非常简单的例子。

方法一： 我们可以把事件监听器做成是Panel的私有内部类

package corejava2.event;

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

public class SimpleButton1 {
	public static void main(String[] args) {
		SimpleFrame1 frame = new SimpleFrame1();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}

/**
 * A frame with a button panel
 */
class SimpleFrame1 extends JFrame {
	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
	
	public SimpleFrame1() {
		setTitle("Simple Button Test");
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
		
		//add panel to frame
		SimplePanel1 panel = new SimplePanel1();
		add(panel);
	}
}

/**
 * A panel with one simple
 */
class SimplePanel1 extends JPanel {
	public SimplePanel1() {
		JButton simpleButton = new JButton("Simple Button");
		add(simpleButton);
		
		ButtonAction buttonAction = new ButtonAction();
		simpleButton.addActionListener(buttonAction);
	}

	/**
	 * An action listener which is an inner class
	 */
	private class ButtonAction implements ActionListener {
		public void actionPerformed(ActionEvent event) {
			JOptionPane.showMessageDialog(null, "You clicked the button!");
		}
	}
}

方法二：我们也可以把事件监听器做成是匿名类

package corejava2.event;

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

public class SimpleButton2 {
	public static void main(String[] args) {
		SimpleFrame2 frame = new SimpleFrame2();
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}
}

/**
 * A frame with a button panel
 */
class SimpleFrame2 extends JFrame {
	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
	
	public SimpleFrame2() {
		setTitle("Simple Button Test");
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);
		
		//add panel to frame
		SimplePanel2 panel = new SimplePanel2();
		add(panel);
	}
}

/**
 * A panel with one simple
 */
class SimplePanel2 extends JPanel {
	public SimplePanel2() {
		JButton simpleButton = new JButton("Simple Button");
		add(simpleButton);
		
		simpleButton.addActionListener(new ActionListener() {
			public void actionPerformed(ActionEvent event) {
				JOptionPane.showMessageDialog(null, "You clicked the button!");
			}
		});
	}

	
}

我们再把这个案例扩充一下，我们可以给事件监听器传入参数，案例如下：

package corejava2.event;

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

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

/**
 * A frame with a button panel
 */
class ButtonFrame extends JFrame {
	public static final int DEFAULT_WIDTH = 300;
	public static final int DEFAULT_HEIGHT = 200;
	
	public ButtonFrame() {
		setTitle("ButtonTest");
		setSize(DEFAULT_WIDTH, DEFAULT_HEIGHT);

		// add panel to frame
		ButtonPanel panel = new ButtonPanel();
		add(panel);
	}
}

/**
 * A panel with three buttons.
 */
class ButtonPanel extends JPanel {
	public ButtonPanel() {
		// create buttons
		JButton yellowButton = new JButton("Yellow");
		JButton blueButton = new JButton("Blue");
		JButton redButton = new JButton("Red");
		
		// add buttons to panel
		add(yellowButton);
		add(blueButton);
		add(redButton);

		// create button actions
		ColorAction yellowAction = new ColorAction(Color.YELLOW);
		ColorAction blueAction = new ColorAction(Color.BLUE);
		ColorAction redAction = new ColorAction(Color.RED);

		// associate actions with buttons
		yellowButton.addActionListener(yellowAction);
		blueButton.addActionListener(blueAction);
		redButton.addActionListener(redAction);
	}

	/**
	 * An action listener that sets the panel's background color.
	 */
	private class ColorAction implements ActionListener {
		private Color backgroundColor;

		public ColorAction(Color c) {
			backgroundColor = c;
		}

		public void actionPerformed(ActionEvent event) {
			String mColor = "";

			setBackground(backgroundColor);
			if (backgroundColor == Color.YELLOW)
				mColor = "Yellow";
			else if (backgroundColor == Color.BLUE)
				mColor = "Blue";
			else if (backgroundColor == Color.RED)
				mColor = "Red";

			JOptionPane.showMessageDialog(null, "You choosed " + mColor + " button");
		}

	}
}