java - 测试游戏的简单功能，无法让物体跳跃

Question

当您按下向上箭头键时，我试图让球上下弹跳。我可以让球向上移动，但它不会停止向上移动。我已经在更新方法中编写了球运动的代码。我试图让球停在 y 坐标 400 处，但它只是将其向上传递。

import javax.swing.*;
import java.awt.*;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.awt.image.DataBufferInt;

public class Game extends Canvas implements Runnable {

int x,y;
public static int width = 300;
public static int height = width / 16 * 9;
public static int scale = 3;
private boolean running = false;

public Thread thread;
public JFrame frame;
public Keyboard key;

private BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
private int[] pixels = ((DataBufferInt)image.getRaster().getDataBuffer()).getData();

public Game() {
    Dimension size = new Dimension(width * scale, height * scale);
    setPreferredSize(size);

    frame = new JFrame();
    key = new Keyboard();
    addKeyListener(key);
}

public synchronized void start() {
    running = true;
    thread = new Thread(this, "Display");
    thread.start();
}

public synchronized void stop(){
    running = false;
    try {
        thread.join();
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

@Override
public void run() {

    long lastTime = System.nanoTime();
    final double nanoSeconds = 1000000000.0 / 60.0;
    double delta = 0;
    int frames = 0;
    int gameUpdates = 0;
    long timer = System.currentTimeMillis();
    requestFocus();

    while(running){

        long now = System.nanoTime();
        delta += (now - lastTime) / nanoSeconds;
        lastTime = now;
        //this ensures that delta only updates the screen 60 times each second
        while (delta >= 1){
            update();
            gameUpdates++;
            delta--;
        }
        render();
        frames++;

        //this if statement happens once a second
        if (System.currentTimeMillis() - timer > 1000){
            timer += 1000;
            frame.setTitle("Bouncy Ball!  ~ ~ ~  Updates per second: " + gameUpdates + ". Frames per second: " + frames + ".");
            gameUpdates = 0;
            frames = 0;
        }
    }
    stop();
}

int yy;

public void update() {
    key.update();

    y = y + yy;

   if(key.up){
       yy = -5;
       if(y == 400){
           yy = 0;}

   }
}

public void render() {
    BufferStrategy bs = getBufferStrategy();
    if (bs == null){
        createBufferStrategy(3);
        return;
    }

    Graphics g = bs.getDrawGraphics();

    g.drawImage(image,0,0,getWidth(),getHeight(),null);

    g.setColor(Color.DARK_GRAY);
    g.fillRect(0,0,getWidth(),getHeight());

    g.setColor(Color.MAGENTA);
    g.fillOval(300,y+435,50,50);


    g.dispose();
    bs.show();
}

public static void main(String[] args) {

    Game game = new Game();
    game.frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    game.frame.setResizable(false);
    game.frame.setVisible(true);
    game.frame.add(game);
    game.frame.pack();
    game.frame.setTitle("Bouncy Ball");

    game.start();
}
}

这是我的 keylisener 类

import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;

public class Keyboard implements KeyListener{

private boolean[] keys = new boolean[120];
public boolean up, down, left, right;

public void update(){

    up = keys[KeyEvent.VK_UP];
    down = keys[KeyEvent.VK_DOWN];
    left = keys[KeyEvent.VK_LEFT];
    right = keys[KeyEvent.VK_RIGHT];

}

@Override
public void keyPressed(KeyEvent e) {
   keys[e.getKeyCode()] = true;
}

@Override
public void keyReleased(KeyEvent e) {
    keys[e.getKeyCode()] = false;
}


@Override
public void keyTyped(KeyEvent e) {

}

}

Answer 1

您的问题出在 key.update() 方法中。 key.up 仅当您按住向上键时才为 true，而不仅仅是按一次向上键。如果现在您只关心按下一个按钮，请将其更改为:

public void update() {
    if (keys[KeyEvent.VK_UP]) {
        up = true;
    }
}

一旦你按下向上键，它只会更新一次，并且keys.up将保持true。

此外，y 正在减少，而不是增加(您要从中减去 5)，因此您想要更改 == 400至== 400 ，或者更好，<= 400 ，以防您不增加整数(按照其他答案)。

作为一般的调试思路:在那个 if 语句中，我打印出了 y 的值，并注意到它只打印了 3 或 4 个值(对应于我按住它的时间)，这意味着 if 语句没有被检查，或者没有返回 true(这里就是这种情况)。