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<html><head><title>JAVA编程语言</title><meta http-equiv="Content-Type" content="text/html; charset=gb2312"><link rel="stylesheet" href="../../../css/text.css" type="text/css"></head><body bgcolor="#FFFFFF" text="#000000" leftmargin="0" topmargin="0" marginwidth="0" marginheight="0" ><table width="100%" border="0" cellpadding="0" cellspacing="0" bgcolor="#FFFFFF"> <tr> <td valign="top"> <table width="100%" border="0" cellspacing="0" cellpadding="0" align="center" bgcolor="#FFFFFF"> <tr> <td valign="top"> <img src="../../../images/html/liti.gif" width="38" height="38" align="absbottom" title="例题"><span class="pt9-black"><font color="000099">例5.10 </font><br> import java.awt.*;<br> import java.awt.event.*;<br> public class ThreeListener implements MouseMotionListener,MouseListener,WindowListener { <br> <font color="339900">//实现了三个接口</font><br> private Frame f;<br> private TextField tf; <br> public static void main(String args[])<br> {<br> ThreeListener two = new ThreeListener();<br> two.go(); } </span> <p class="pt9-black"> public void go() {<br> f = new Frame("Three listeners example"); <br> f.add(new Label("Click and drag the mouse"),"North");<br> tf = new TextField(30);<br> f.add(tf,"South"); <font color="339900">//使用缺省的布局管理器</font><br> f.addMouseMotionListener(this); <font color="339900">//注册监听器MouseMotionListener</font><br> f.addMouseListener(this); <font color="339900">//注册监听器MouseListener</font><br> f.addWindowListener(this); <font color="339900">//注册监听器WindowListener</font><br> f.setSize(300,200);<br> f.setVisible(true); <br> }</p> <p class="pt9-black"> public void mouseDragged (MouseEvent e) { <br> <font color="339900">//实现mouseDragged方法</font><br> String s = "Mouse dragging : X="+e.getX()+"Y = "+e.getY();<br> tf.setText(s);<br> }<br> public void mouseMoved(MouseEvent e){} <br> <font color="339900">//对其不感兴趣的方法可以方法体为空</font><br> public void mouseClicked(MouseEvent e){}<br> public void mouseEntered(MouseEvent e){<br> String s = "The mouse entered";<br> tf.setText(s);<br> }</p> <p class="pt9-black"> public void mouseExited(MouseEvent e){<br> String s = "The mouse has left the building";<br> tf.setText(s);<br> } <br> <br> public void mousePressed(MouseEvent e){}<br> public void mouseReleased(MouseEvent e){ }<br> public void windowClosing(WindowEvent e) { <br> <font color="339900">//为了使窗口能正常关闭，程序正常退出，需要实现windowClosing方法</font><br> System.exit(1);<br> }</p> <p class="pt9-black"> public void windowOpened(WindowEvent e) {} <br> <font color="339900">//对其不感兴趣的方法可以方法体为空</font><br> public void windowIconified(WindowEvent e) {}<br> public void windowDeiconified(WindowEvent e) {}<br> public void windowClosed(WindowEvent e) {}<br> public void windowActivated(WindowEvent e) { }<br> public void windowDeactivated(WindowEvent e) {}</p> <p class="pt9-black"> }</p> <p><span class="pt9-black"> 上例中有如下几个特点：<br> 1．可以声明多个接口，接口之间用逗号隔开。<br> ……implements MouseMotionListener, MouseListener, WindowListener；<br> <br> 2．可以由同一个对象监听一个事件源上发生的多种事件：<br> f.addMouseMotionListener(this);<br> f.addMouseListener(this);<br> f.addWindowListener(this);<br> 则对象f 上发生的多个事件都将被同一个监听器接收和处理。<br> <br> 3．事件处理者和事件源处在同一个类中。本例中事件源是Frame f，事件处理者是类ThreeListener，其中事件源Frame f是类ThreeListener的成员变量。<br> <br> 4．可以通过事件对象获得详细资料，比如本例中就通过事件对象获得了鼠标发生时的坐标值。<br> public void mouseDragged(MouseEvent e) {<br> String s="Mouse dragging :X="+e.getX()+"Y="+e.getY();<br> tf.setText(s);<br> }<br> <br> <font color="000099"> Java语言类的层次非常分明，因而只支持单继承，为了实现多重继承的能力，Java用接口来实现，一个类可以实现多个接口，这种机制比多重继承具有更简单、灵活、更强的功能。在AWT中就经常用到声明和实现多个接口。记住无论实现了几个接口，接口中已定义的方法必须一一实现，如果对某事件不感兴趣，可以不具体实现其方法，而用空的方法体来代替。但却必须所有方法都要写上。<br> </font> </span> </p> <p class="pt9-black"> </p> </td> </tr> </table> </td> </tr></table></body></html>⌨️ 快捷键说明
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