Main.GamePanel不是抽象的，并且不会覆盖java.awt.event.KeyListener中的抽象方法keyReleased（java.awt.event.KeyEvent）

Question

I was doing a tutorial online because I wanted to make a 2d side scroller, and I got this exact error. I have googled it but came up with nothing. I tried looking for a typo and it looks clean, its not giving me an error anywere else in the code. I do not know where to start. If you could explaing to me what the error is and how i fix it then that would be amazing.

    package Main;


import GameState.GameStateManager;
import javax.swing.JPanel;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.image.BufferedImage;

public class GamePanel extends JPanel implements Runnable, KeyListener{
    public static final int WIDTH = 320;
    public static final int HIGHT = 240;
    public static final int SCALE = 2;

    //game thread

    private Thread thread;
    private boolean running;
    private int FPS = 60;
    private long targetTime = 1000/FPS;
    //image        
    private BufferedImage image;
    private Graphics2D g;

    //game state manager
    private GameStateManager gsm;




    public GamePanel(){
        super();
        setPreferredSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
        setFocusable(true);
        requestFocus();
    }
    public void addNotify(){
        super.addNotify();
        if (thread == null) {
            thread = new Thread(this);
            addKeyListener(this);
            thread.start();
        }
    }   
    private void init() {
        image = new BufferedImage(WIDTH, HIGHT, BufferedImage.TYPE_INT_RGB);     
        g = (Graphics2D) image.getGraphics();
        running = true;
        gsm = new GameStateManager();

    }

        public void run(){
        init();
        long start, elapsed, wait;

        //game loop
          while(running) {

            start = System.nanoTime();
            update();
            draw();
            drawToScreen();
               elapsed = System.nanoTime() - start;

               wait = targetTime - elapsed / 1000000;

               try
               {
                   Thread.sleep(wait);
               }
               catch(Exception e) 
               {
                   e.printStackTrace();
               }//end of try catch
          }







        }
        private void update()
        {
            gsm.update();
        }
        private void draw()
        {
            gsm.draw(g);
        }
        private void drawToScreen()
        {
            Graphics g2 = getGraphics();
            g2.drawImage(image, 0, 0, null);
            g2.dispose();


        }




        public void KeyPressed(KeyEvent key) 
        {
         gsm.keyPressed(key.getKeyCode());
        }
        public void KeyReleased(KeyEvent key) 
        {
         gsm.keyReleased(key.getKeyCode());
        }




    }

Answer 1

The compiler error message tells you exactly what's wrong: your class implements the KeyListener interface but does not implement all the necessary methods of the interface. Solution: be sure to implement all the necessary methods as per the KeyListener API. Also be sure to use the @Override annotation to make sure that your overrides are correct.

Having said that, I'm going to recommend that you not use KeyListeners for most key board input with Swing applications, that it is a low-level listener and should be avoided in favor of higher level constructs such as key bindings . Also, Swing GUI's should avoid use of update(...) method overrides as that is more of an AWT construct.

Answer 2

Your KeyReleased(KeyEvent key) method must start with small letter 'k' like keyReleased(KeyEvent key) . Java is case sensitive.

You may also required to override other methods of KeyListener interface.

Also add @Override annotation (as suggested by @Hovercraft Full Of Eels) to the method when you want to override a super method. That way IDE's will give you hint's while coding.