package listener;import java.awt.*;import java.awt.event.*;import javax.swing.*;//使用implements關鍵字加入聚焦接收器public class FocusListenerDemo extends JFrame implements FocusListener {  JPanel contentPane;   //創建3個編輯框  JTextField jTextField1 = new JTextField();  JTextField jTextField2 = new JTextField();  JTextField jTextField3 = new JTextField();  //創建3個標簽  JLabel jLabel1 = new JLabel();  JLabel jLabel2 = new JLabel();  JLabel jLabel3 = new JLabel();  public static void main(String[] args) {    FocusListenerDemo frame = new FocusListenerDemo();    frame.setVisible(true);  }  public FocusListenerDemo() {    jbInit();  }  private void jbInit() {    contentPane = (JPanel)this.getContentPane();    contentPane.setLayout(null);    this.setSize(new Dimension(400, 300));    this.setTitle("聚焦接收器示例");    jTextField1.setBounds(new Rectangle(184, 48, 143, 29));    //加入聚焦接收器    jTextField1.addFocusListener(this);    jTextField2.setBounds(new Rectangle(184, 116, 143, 29));    jTextField2.addFocusListener(this);    jTextField3.setBounds(new Rectangle(184, 183, 143, 29));    jTextField3.addFocusListener(this);    jLabel1.setText("編輯框1");    jLabel1.setBounds(new Rectangle(63, 48, 79, 16));    jLabel2.setText("編輯框2");    jLabel2.setBounds(new Rectangle(63, 116, 61, 16));    jLabel3.setText("編輯框3");    jLabel3.setBounds(new Rectangle(63, 183, 86, 16));    contentPane.add(jTextField1, null);    contentPane.add(jTextField2, null);    contentPane.add(jTextField3, null);    contentPane.add(jLabel1, null);    contentPane.add(jLabel2, null);    contentPane.add(jLabel3, null);  }  //當主窗口關閉時,清空內存  protected void processWindowEvent(WindowEvent e) {    if (e.getID() == WindowEvent.WINDOW_CLOSING) {      System.exit(0);    }  }  //當控件獲得焦點時,執行下面代碼  public void focusGained(FocusEvent e) {    displayMessage("獲得焦點", e);  }  //當按件失去焦點時,執行下面代碼  public void focusLost(FocusEvent e) {    displayMessage("失去焦點", e);  }  //顯示信息方法  void displayMessage(String infor, FocusEvent e) {    //取得激發聚焦事件的控件    JTextField tempTextField = (JTextField)e.getSource();    //截取控件的名稱,將控件的其它屬性刪除    JOptionPane.showMessageDialog(null, componentStr.substring(0, componentStr.indexOf("["))                       + infor + "\n");  }}