一、事件监听机制
-- 事件源：awt 或swing包中的那些图形界面组件,即发生事件的组件
-- 事件：Event 用户对组件的一个操作
-- 监听器：Listener 负责处理事件的方法
二、java.awt.event 包下的类
WindowEvent //窗口事件,比如用户点了半闭窗口,窗口得到或失去焦点,最大化最小化等
MouseEvent //鼠标事件,鼠标按下,鼠标释放,点击(按下后再松开)等
ActionEvent //动作事件,它不是代表一个具体动作,而是一种语义,比如按纽,或菜单被点击,在文本框中按下回车等,可以这样理解:用户的某一动作导致了某个组件本身的基本作用发生了,这就是ActionEvent事件
不同的事件类型,对应着不同的事件监听器接口,接口的名称和事件的名称是相对应的。
WindowEvent - >WindowListener
MouseEvent ->MouseListener
ActionEvent ->ActionListener
代码示例：
import java.awt.Frame;
import java.awt.event.WindowEvent;
import java.awt.event.WindowListener; public class Test20 {
public static void main(String[] args) {
Frame f = new Frame();
f.setSize(400, 400);
f.setVisible(true); f.addWindowListener(new WindowListener() { @Override
public void windowOpened(WindowEvent e) { // 窗口被打开
// TODO Auto-generated method stub } @Override
public void windowClosing(WindowEvent e) { // 设置关闭事件
// TODO Auto-generated method stub
System.exit(0);
} @Override
public void windowClosed(WindowEvent e) { // 用户已经关闭窗口
// TODO Auto-generated method stub } @Override
public void windowIconified(WindowEvent e) { // 被最小化的时候
// TODO Auto-generated method stub } @Override
public void windowDeiconified(WindowEvent e) { // 最小化被还原的时候
// TODO Auto-generated method stub } @Override
public void windowActivated(WindowEvent e) { // 窗体被激活
// TODO Auto-generated method stub } @Override
public void windowDeactivated(WindowEvent e) { // 失去焦点的时候
// TODO Auto-generated method stub } });
}
}
有没有发现，用WindowListener接口的时候，会引入一大堆不常用的代码（这里我们只想设置关闭），借口里的方法只能被覆盖，又不能删掉，这样就是的整个项目显得很罗嗦，为了解决这个事情，就有了事件适配器。
三、事件适配器
JDK 针对大多数事件监听器接口类定义了相应的实现类（里面有很多空实现的方法，方便我们创建侦听器对象），我们称为事件适配器类。这里我用到了WindowAdapter。
import java.awt.Frame;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent; public class Test21 {
public static void main(String[] args) {
Frame f = new Frame("事件适配器的栗子");
f.setSize(400, 400);
f.setVisible(true); f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
}
}
可以观察一下WindowAdapter类的源码，找找感觉。
public abstract class WindowAdapter
implements WindowListener, WindowStateListener, WindowFocusListener
{
/**
* Invoked when a window has been opened.
*/
public void windowOpened(WindowEvent e) {} /**
* Invoked when a window is in the process of being closed.
* The close operation can be overridden at this point.
*/
public void windowClosing(WindowEvent e) {} /**
* Invoked when a window has been closed.
*/
public void windowClosed(WindowEvent e) {} /**
* Invoked when a window is iconified.
*/
public void windowIconified(WindowEvent e) {} /**
* Invoked when a window is de-iconified.
*/
public void windowDeiconified(WindowEvent e) {} /**
* Invoked when a window is activated.
*/
public void windowActivated(WindowEvent e) {} /**
* Invoked when a window is de-activated.
*/
public void windowDeactivated(WindowEvent e) {} /**
* Invoked when a window state is changed.
* @since 1.4
*/
public void windowStateChanged(WindowEvent e) {} /**
* Invoked when the Window is set to be the focused Window, which means
* that the Window, or one of its subcomponents, will receive keyboard
* events.
*
* @since 1.4
*/
public void windowGainedFocus(WindowEvent e) {} /**
* Invoked when the Window is no longer the focused Window, which means
* that keyboard events will no longer be delivered to the Window or any of
* its subcomponents.
*
* @since 1.4
*/
public void windowLostFocus(WindowEvent e) {}
}
练习几个个事件处理程序的栗子吧。
例一：
import java.awt.Button;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener; //例一：在窗体中放置一个按纽,点击后让程序退出
class TestFrame implements ActionListener { // ActionListener接口里面只有一个方法，下面会重写
private Frame f; public TestFrame() {
f = new Frame("窗口");
init();
} private void init() {
f.setSize(300, 300);
f.setLayout(new FlowLayout());// 布局模式
Button b = new Button("退出程序");
b.addActionListener(this);
f.add(b);
f.setVisible(true); } @Override
public void actionPerformed(ActionEvent e) {
// TODO Auto-generated method stub
f.setVisible(false);
f.dispose();// 在关闭的时候，可以用它来销毁窗体资源
System.exit(0);// 退出
} } public class Test22 {
public static void main(String[] args) {
new TestFrame();
} }
上面的，点击退出程序按钮才可以退出，点击右上角的X，是不可以退出的哦。因为没有设置WindowListener哦。
这个例子用到ActionListener接口，可以看一下它的源代码，如下：
public interface ActionListener extends EventListener {
/**
* Invoked when an action occurs.
*/
public void actionPerformed(ActionEvent e);
}例二：
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.TextField;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent; //在窗体中,放置一个文本框,能过滤非法字符( 除了数字以外的 )
public class TestFrame {
private Frame f;
private TextField txtNo;// TextField代表文本框 public TestFrame() {
f = new Frame("请输入密码"); //f.setBackground(red);这里我自己试的, 没成功
f.setBackground(Color.red);//这样就可以了
f.setBounds(50, 50, 400, 400);// 设置窗口坐标和大小
f.setLayout(new FlowLayout());// 设置窗体布局 txtNo = new TextField(10);// 设置输入窗口的显示长度。输入的内容长度没有界限
f.add(txtNo); txtNo.addKeyListener(new KeyAdapter() {
// 从JDk中粘贴过来这个方法来用
public void keyPressed(KeyEvent e) {
int code = e.getKeyCode();
if (!(code >= KeyEvent.VK_0 && code <= KeyEvent.VK_9)) {// 设置输入内容为0-9
System.out.println(KeyEvent.getKeyText(code) + "输入有误");
e.consume();
}
}
}); f.setVisible(true);
f.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {
f.dispose();
System.exit(0);
}
}); }
}
测试类：
public class Test23 {
public static void main(String[] args) {
new TestFrame();
}
}例三：
列出指定目录的内容：
import java.awt.Button;
import java.awt.FlowLayout;
import java.awt.Frame;
import java.awt.TextArea;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.io.File; public class Test24 {
public static void main(String[] args) {
new MyWindow();
}
} class MyWindow {
MyWindow() {
init();
} private Frame f;
private Button b;
private TextField txtDir;// 用来输入目录名称
private TextArea txtFileList;// 用来显示文件列表 private void init() {
f = new Frame("窗口");
f.setBounds(44, 44, 500, 500);
f.setLayout(new FlowLayout()); txtDir = new TextField(8);
b = new Button("显示");
txtFileList = new TextArea(20, 30);// 用来显示文件列表的区域 f.add(txtDir);
f.add(b);
f.add(txtFileList);
initEvent();
f.setVisible(true);
} private void initEvent() {
// TODO Auto-generated method stub
f.addWindowListener(new WindowAdapter() {
/**
* Invoked when a window is in the process of being closed. The
* close operation can be overridden at this point.
*/
public void windowClosing(WindowEvent e) {
System.exit(0);
}
});
b.addActionListener(new ActionListener() {
/**
* Invoked when an action occurs.
*/
public void actionPerformed(ActionEvent e) {
txtFileList.setText("");
String dirStr = txtDir.getText();// 取出用户输入的路径
File file = new File(dirStr);
if (file.isDirectory() && file.exists()) {
String[] fileNameList = file.list(); for (String s : fileNameList) {
txtFileList.append(s + "\r\n");// 别忘了换行符
}
} else {
txtFileList.append("输入有误，请重新输入");
}
}
}); }
}
结果：（我让它显示我D盘的目录）