java - 将 KeyListener 添加到 JLabel

Question

我想让一个类从 JLabel 扩展并实现 KeyListener，但是 KeyListener 不起作用。现在 MouseListener 工作但 KeyListner 不工作，但为什么？另一个问题是当将 JFrame 的布局设置为 null 时，它不显示(图像汽车或汽车对象)。

    public class car extends JLabel implements KeyListener,MouseListener{
        private ImageIcon imgico;//to set Image icon of car
        public car(int car_num,boolean line1,Dimension position){
            //car_num variable check which of Image of car load
            //if line1 is true .line 1 else car load in line 2
            super();
            this.imgico = this.car_load(car_num, line1);
            super.setIcon(this.imgico);
            super.setVisible(true);
            super.setSize(this.imgico.getIconWidth(),this.imgico.getIconHeight());
            super.setLocation(position.width, position.height);
            this.addKeyListener(this);
            this.addMouseListener(this);

        }
        private ImageIcon car_load(int car_num,boolean line1){
            //load image icon of car
            if (car_num == 1 && line1 == true)
                return (new ImageIcon("Images/cars/01a.PNG"));
            else if (car_num == 1 && line1 == false)
                return (new ImageIcon("Images/cars/01b.PNG"));
            else if (car_num == 2 && line1 == true)
                return (new ImageIcon("Images/cars/02a.PNG"));
            else if (car_num == 2 && line1 == false)
                return (new ImageIcon("Images/cars/02b.PNG"));
            else if (car_num == 3 && line1 == true)
                return (new ImageIcon("Images/cars/03a.PNG"));
            else if (car_num == 3 && line1 == false)
                return (new ImageIcon("Images/cars/03b.PNG"));
            else if (car_num == 4 && line1 == true)
                return (new ImageIcon("Images/cars/04a.PNG"));
            else if (car_num == 4 && line1 == false)
                return (new ImageIcon("Images/cars/04b.PNG"));
            else if (car_num == 5 && line1 == true)
                return (new ImageIcon("Images/cars/05a.PNG"));
            else if (car_num == 5 && line1 == false)
                return (new ImageIcon("Images/cars/05b.PNG"));
            else if (car_num == 6 && line1 == true)
                return (new ImageIcon("Images/cars/06a.PNG"));
            else
                return (new ImageIcon("Images/cars/06b.PNG"));
            // by deafult its 06b 
        }
        @Override
        public void keyPressed(KeyEvent arg0) {
            // TODO Auto-generated method stub
            System.out.println(arg0.getKeyCode());
        }
        @Override
        public void keyReleased(KeyEvent arg0) {
            // TODO Auto-generated method stub

        }
        @Override
        public void keyTyped(KeyEvent arg0) {
            // TODO Auto-generated method stub
            System.out.println(arg0.getKeyCode());

        }
        @Override
        public void mouseClicked(MouseEvent arg0) {
            if (arg0.getSource() == this)
                System.out.println("Hi");
        }
        @Override
        public void mouseEntered(MouseEvent arg0) {
            // TODO Auto-generated method stub

        }
        @Override
        public void mouseExited(MouseEvent arg0) {
            // TODO Auto-generated method stub

        }
        @Override
        public void mousePressed(MouseEvent arg0) {
            // TODO Auto-generated method stub

        }
        @Override
        public void mouseReleased(MouseEvent arg0) {
            // TODO Auto-generated method stub

        }
    }

主要内容:

    JFrame x = new JFrame();
    x.setSize(500,500);
    x.setVisible(true);
    Dimension v = new Dimension(5,5);
    car t =new car(1,true,v);
    x.setLayout(null);
    x.add(t);

Answer 1

我不认为 JLabel 可以获得焦点，因此永远不会触发 KeyEvent。看这个documentation了解更多详情。