SWING - FocusListener 介面

簡介

介面 FocusListener 用於接收鍵盤焦點事件。處理焦點事件的類需要實現此介面。

類宣告

以下是 java.awt.event.FocusListener 介面的宣告 -

public interface FocusListener
extends EventListener

介面方法

繼承的方法

此類從以下介面繼承了方法 -

java.awt.event.EventListener

FocusListener 示例

在D:/ > SWING > com > tutorialspoint > gui > 中使用任意編輯器建立以下 Java 程式

SwingListenerDemo.java

package com.tutorialspoint.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. ");
      }
   }
}

使用命令提示符編譯程式。轉到 D:/ > SWING 並鍵入以下命令。

D:\SWING>javac com\tutorialspoint\gui\SwingListenerDemo.java

如果未發生錯誤，則表示編譯成功。使用以下命令執行程式。

D:\SWING>java com.tutorialspoint.gui.SwingListenerDemo

驗證以下輸出。