我对java相对较新，我无法弄清楚Pong的键盘按下

Question

• 我正在为一个类项目制作Pong，我不知道如何使用键盘输入。我在网上看了很多指南，但我做的都不管用。知道为什么它没有注册任何键盘输入吗？我很确定我有所有正确的进口产品。

  package pong2;
  import java.awt.color.*;
  import javax.swing.JFrame;
  import java.awt.Canvas;
  import java.awt.Color;
  import java.awt.Graphics;
  import java.awt.event.KeyEvent;
  import java.awt.event.KeyListener;
  import java.util.logging.Level;
  import java.util.logging.Logger;
  
  public class graphic extends Canvas implements KeyListener 
  {
  int y1 = 450;
  int y2 = 450;
  public static void main(String[] args) throws InterruptedException 
  {   
  

• JFrame

  JFrame frame = new JFrame("Pong");
  Canvas canvas = new graphic();
  canvas.setSize(1920,1080);
  frame.add(canvas);
  frame.setBackground(Color.BLACK);
  frame.pack();
  frame.setVisible(true);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.addKeyListener(new KeyListener() );
  frame.repaint();
  }
  

• 密钥侦听器

  @Override
  public void  keyTyped(KeyEvent e) 
  {
  //System.out.println("Key Typed");
  }
  @Override
  public void keyPressed(KeyEvent e) 
  {
  if(e.getKeyCode() == KeyEvent.VK_DOWN); 
  {
  //System.out.println("Key Pressed " + e.getKeyCode());
  y2 = y2 - 10;
  repaint();
  }       
  if(e.getKeyCode() == KeyEvent.VK_UP);
  {
  y2 = y2 + 10;
  repaint();
  }
  }
  @Override
  public void keyReleased(KeyEvent e) 
  {
  //System.out.println("Key Released");
  }
  

• 乒乓板图形

  public void paint(Graphics g) 
  {
  super.paint(g);
  //Background
  g.setColor(Color.BLACK);
  g.fillRect(0,0,1920,1080);
  //Goals
  g.setColor(Color.WHITE);
  g.fillRect(0,0,50,1080);
  g.fillRect(1870,0,50,1080);
  //Paddles
  g.fillRect(120,y1,20,150);
  g.fillRect(1790,y2,20,150);
  //Ball
  g.fillRect(950,525,20,20);
  }
  
  }
  

Answer 1

由于graphic类扩展了Canvas并实现了KeyListener，并且Canvas引用指向graphic对象i-eCanvas canvas = new graphic();

因此，您必须注册canvas才能监听键盘输入。

更改frame.addKeyListener(new KeyListener())

至

frame.addKeyListener((KeyListener) canvas);

或

frame.addKeyListener((graphic) canvas);