接口focusListener的用于接收键盘焦点事件。过程焦点事件的类需要实现这个接口。

类声明

以下是声明 java.awt.event.FocusListener接口：

public interface FocusListener
extends EventListener

接口方法

S.N.	方法 & 描述
1	void focusGained(FocusEvent e) Invoked when a component gains the keyboard focus.
2	void focusLost(FocusEvent e) Invoked when a component loses the keyboard focus.

方法继承

这个类方法从下面的接口继承：

• java.awt.event.EventListener

FocusListener 例子

选择使用任何编辑器创建以下java程序在 D:/ > SWING > com > yiibai > gui >

SwingListenerDemo.java

package com.yiibai.gui;

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

public class SwingListenerDemo {
   private JFrame mainFrame;
   private JLabel headerLabel;
   private JLabel statusLabel;
   private JPanel controlPanel;

   public SwingListenerDemo(){
      prepareGUI();
   }

   public static void main(String[] args){
      SwingListenerDemo  swingListenerDemo = new SwingListenerDemo();  
      swingListenerDemo.showFocusListenerDemo();
   }

   private void prepareGUI(){
      mainFrame = new JFrame("Java SWING Examples");
      mainFrame.setSize(400,400);
      mainFrame.setLayout(new GridLayout(3, 1));

      headerLabel = new JLabel("",JLabel.CENTER );
      statusLabel = new JLabel("",JLabel.CENTER);        

      statusLabel.setSize(350,100);
      mainFrame.addWindowListener(new WindowAdapter() {
         public void windowClosing(WindowEvent windowEvent){
	        System.exit(0);
         }        
      });    
      controlPanel = new JPanel();
      controlPanel.setLayout(new FlowLayout());

      mainFrame.add(headerLabel);
      mainFrame.add(controlPanel);
      mainFrame.add(statusLabel);
      mainFrame.setVisible(true);  
   }
   private void showFocusListenerDemo(){

      headerLabel.setText("Listener in action: FocusListener");      
      JButton okButton = new JButton("OK");
      JButton cancelButton = new JButton("Cancel");
   
      okButton.addFocusListener(new CustomFocusListener());  
      cancelButton.addFocusListener(new CustomFocusListener());  
   
      controlPanel.add(okButton);
      controlPanel.add(cancelButton);     
      mainFrame.setVisible(true);  

   }

   class CustomFocusListener implements FocusListener{
      public void focusGained(FocusEvent e) {
         statusLabel.setText(statusLabel.getText() 
         + e.getComponent().getClass().getSimpleName() + " gained focus. ");
      }

      public void focusLost(FocusEvent e) {
         statusLabel.setText(statusLabel.getText() 
         + e.getComponent().getClass().getSimpleName() + " lost focus. ");
      }
   }
}

编译程序，使用命令提示符。到 D:/ > SWING 然后输出以下命令。

D:SWING>javac comyiibaiguiSwingListenerDemo.java

如果没有错误出现，这意味着编译成功。使用下面的命令来运行程序。

D:SWING>java com.yiibai.gui.SwingListenerDemo

验证下面的输出