Java基础——GUI编程（二）

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 + "
");// 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）