FocusListener焦点监听器

public class Demo extends JFrame {
    public Demo(){
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        setBounds(100,100,200,120);

        Container c=getContent();
        JTextField sk1=new JTextField();
        JTextField sk2=new JTextField();
         JTextField sk3=new JTextField();
         sk1.setColumns(15);
         sk2.setColumns(15);
         sk3.setColumns(15);
         c.add(sk1);
         c.add(sk2);
         c.add(sk3);
         sk1.FocusListener(new myFocusListener );//调用自定义焦点监听方法类
         sk2.FocusListener(new myFocusListener );
         sk3.FocusListener(new myFocusListener );
         setVisible(true);
     
//在myFocusListener 上 ，按Alt+Enter导入Java类快捷键 implements FocusListener
      class  myFocusListener implements FocusListener{//实现焦点监听 有光标点击为绿色，无光标点击为红色。
     @Override
        public void focusGained(FocusEvent e) {
          JTextField sk=(JTextField) e.getSource();//获取触发焦点事件的控件，强制转换为文本
           jt.setBorder(BorderFactory.createLineBorder(Color.green));
        }

        @Override
        public void focusLost(FocusEvent e) {
          JTextField sk=(JTextField) e.getSource();//获取焦点事件触发的控件。强制转换为文本
            jt.setBorder(BorderFactory.createLineBorder(Color.RED));
        }
    }
    public static void main(String[] args) {
        new Demo();
    }
}