问Java - KeyListener - KeyReleased有时不会触发

EN

package input;

import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import game.Game;

public class KeyboardInput extends KeyAdapter {
   public KeyboardInput() {
   }

   // Detects pressed keys
   public void keyPressed(KeyEvent e) {
      if (Game.init) {
         Keys.Keys[e.getKeyCode()] = true;
      }
   }

   // Detects released keys
   public void keyReleased(KeyEvent e) {
      if (Game.init) {
         Keys.Keys[e.getKeyCode()] = false;
      }
   } 
}

 // Display Constructor
public Display(String title, String gameVersion, int width, int height) {
  this.title = title;
  this.width = width;
  this.height = height;
  this.gameVersion = gameVersion;

  createDisplay();
}

// Creates display
private void createDisplay() {
  frame = new JFrame(title + " v. " + gameVersion);
  frame.setSize(width, height);
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  frame.setResizable(false);
  frame.setLocationRelativeTo(null);
  frame.setVisible(true);
  frame.setFocusable(true);

  canvas = new Canvas();
  canvas.setPreferredSize(new Dimension(width, height));
  canvas.setMinimumSize(new Dimension(width, height));
  canvas.setMaximumSize(new Dimension(width, height));
  canvas.setBackground(Color.WHITE);

  frame.add(canvas);
  frame.addKeyListener(new KeyboardInput()); // ADDING KEY LISTENER TO THE JFRAME
  canvas.addMouseListener(new MouseInput());
  frame.pack();
  if (frame.getKeyListeners().length > 0) {
    System.out.println("Key listener initialized");
  } else {
    System.out.println("ERROR : Key listener couldn't initialize");
  }
  if (canvas.getMouseListeners().length > 0) {
    System.out.println("Mouse listener initialized");
  } else {
    System.out.println("ERROR : Mouse listener couldn't initialize");
  }
}

// Updates display (called every frame)
public void update() {
  frame.requestFocus();
  tick++;
  lasttime = currtime;
  currtime = System.nanoTime();
  delta = (currtime - lasttime) / 1000000000;
  fps = (float) (1 / delta);
  if ((tick / fps) >= SAVE_TIME) {
    tick = 0;
    saveNextTick = true;
    System.out.println("FPS = " + Math.round(getFPS()));
    try {
      System.out.println("MOUSE POSITION = (" + frame.getMousePosition().getX() + ", "
        + frame.getMousePosition().getY() + ")");
    } catch (Exception e) {
      System.out.println("Mouse out of screen. Could not get mouse position (NullPointerException)");
    }
  }

  if (saveNextTick) {
    Save.saveGame("Save");
    saveNextTick = false;
  }
}

private void checkMove() {
   int speed = moveSpeed;
   int x1 = getxPos();
   int x2 = x1 + getTexture().getImage().getWidth();
   int y1 = getyPos();
   int y2 = y1 + getTexture().getImage().getHeight();
   if ((Keys.Keys[KeyEvent.VK_W] || Keys.Keys[KeyEvent.VK_S]) &&       (Keys.Keys[KeyEvent.VK_A] || Keys.Keys[KeyEvent.VK_D])) {
      speed = diagonalMoveSpeed;
   }
   int d = Math.max((int) (speed / Display.getFPS()), 1);
   if (speed / Display.getFPS() < 1 && Util.randInt(0, 100) > speed /  Display.getFPS() * 100) {
      d = 0;
   }
   if (Keys.Keys[KeyEvent.VK_W] && !States.currentState.checkCollision(x1,  x2, y1 - d, y2 - d)) {
      move(0, -d);
   }
   if (Keys.Keys[KeyEvent.VK_A] && !States.currentState.checkCollision(x1 - d, x2 - d, y1, y2)) {
      move(-d, 0);
   }
   if (Keys.Keys[KeyEvent.VK_S] && !States.currentState.checkCollision(x1, x2, y1 + d, y2 + d)) {
      move(0, d);
   }
   if (Keys.Keys[KeyEvent.VK_D] && !States.currentState.checkCollision(x1 + d, x2 + d, y1, y2)) {
      move(d, 0);
   }
}