Java贪吃蛇游戏: Apple showing while snake is invisible

Question

我正在按照以下视频来设计贪吃蛇游戏: https://www.youtube.com/watch?v=91a7ceECNTc

我正在一步一步地跟踪它，但是当我运行它时，蛇没有显示在我的屏幕上，只显示苹果。我认为在实现 public void Paint(Graphics g); 时出现问题，有人可以帮助我吗？

这是我的主类的代码

import javax.swing.JFrame;
public class Main {

public static void main(String[] args) {
    JFrame frame = new JFrame ();
    GamePanel panel = new GamePanel();

    frame.add(panel);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setTitle("Snake");

    frame.pack();
    frame.setVisible(true);
    frame.setLocationRelativeTo(null);
}
}

这是面板类:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JPanel;

public class GamePanel extends JPanel implements Runnable, KeyListener{

private static final long serialVersionUID = 1L;
public static final int WIDTH = 1000, HEIGHT = 1000; //Dimensions of the panel (Will be set by user input later)
private Thread thread;
private boolean running;
private boolean right = true, left = false, up = false, down = false;

private BodyPart b;
private ArrayList<BodyPart> snake;
private Apple apple;
private ArrayList<Apple> apples;
private Random r;

private int xCoor = 100, yCoor = 100, size = 10;
private int ticks = 0;

public GamePanel() {
    setFocusable(true);
    setPreferredSize(new Dimension(WIDTH, HEIGHT));
    addKeyListener(this);
    snake = new ArrayList<BodyPart>();
    apples = new ArrayList<Apple>();
    r = new Random();
    start();

}
public void start() {
    running = true;
    thread = new Thread(this);
    thread.start();
}
public void stop() {
    running = false;
    try {
        thread.join();
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}
public void tick() {
    if (snake.size() == 0) {
        b = new BodyPart(xCoor, yCoor, 10);
        snake.add(b);
    }
    ticks++;
    if (ticks > 250000) {
        if (right) {
            xCoor++;
        }
        if (left) {
            xCoor--;
        }
        if (up) {
            yCoor--;
        }
        if (down) {
            yCoor++;
        }
        ticks = 0;
        b = new BodyPart(xCoor, yCoor, 10);
        snake.add(b);
        if (snake.size() > size) {
            snake.remove(0);
        }
    }
    if (apples.size() == 0) {
        int xCoor = r.nextInt(99);
        int yCoor = r.nextInt(99);
        apple = new Apple(xCoor, yCoor, 10);
        apples.add(apple);
    }
}
public void paint(Graphics g) {

    g.clearRect(0, 0, WIDTH, HEIGHT);
    g.setColor(Color.BLACK);
    g.fillRect(0, 0, WIDTH, HEIGHT);

    for (int i = 0; i < WIDTH/10; i++) {
        g.drawLine(i*10, 0, i*10, HEIGHT);
    }
    for (int i = 0; i < HEIGHT/10; i++) {
        g.drawLine(0, i*10, HEIGHT, i*10);
    }
    for (int i = 0; i < snake.size(); i++) {
        snake.get(i).draw(g);
    }
    for (int i = 0; i < apples.size(); i++) {
        apples.get(i).draw(g);
    }
}

@Override
public void run() {
    while (running) {
        tick();
        repaint();
    }
}
@Override
public void keyTyped(KeyEvent e) {
    int key = e.getKeyCode();
    if (key == KeyEvent.VK_RIGHT && !left) {
        right = true;
        up = false;
        down = false;
    }
    if (key == KeyEvent.VK_LEFT && !right) {
        left = true;
        up = false;
        down = false;
    }
    if (key == KeyEvent.VK_UP && !down) {
        up = true;
        right = false;
        left = false;
    }
    if (key == KeyEvent.VK_DOWN && !up) {
        down = true;
        right = false;
        left = false;
    }

}
@Override
public void keyPressed(KeyEvent e) {
    // TODO Auto-generated method stub

}
@Override
public void keyReleased(KeyEvent e) {
    // TODO Auto-generated method stub

}
}

蛇的 body 部位类别:

import java.awt.Color;
import java.awt.Graphics;

public class BodyPart {
public int xCoor, yCoor, width, height;

public BodyPart(int xCoor, int yCoor, int tileSize) {
    this.xCoor = xCoor;
    this.yCoor = yCoor;
    width = tileSize;
    height = tileSize;
}
public void tick() {

}
public void draw(Graphics g) {
    g.setColor(Color.YELLOW);
    g.fillRect(xCoor * width, yCoor * height, width, height);
}
public int getCoorX() {
    return xCoor;
}
public void setCoorX (int xCoor) {
    this.xCoor = xCoor;
}
public int getCoorY() {
    return yCoor;
}
public void setCoorY(int yCoor) {
    this.yCoor = yCoor;
}
}

还有苹果的类(class):

import java.awt.Color;
import java.awt.Graphics;

public class Apple {
public int xCoor, yCoor, width, height;

public Apple(int xCoor, int yCoor, int tileSize) {
    this.xCoor = xCoor;
    this.yCoor = yCoor;
    width = tileSize;
    height = tileSize;
}
public void tick() {

}
public void draw(Graphics g) {
    g.setColor(Color.RED);
    g.fillRect(xCoor * width, yCoor * height, width, height);
}
public int getxCoor() {
    return xCoor;
}
public void setxCoor(int xCoor) {
    this.xCoor = xCoor;
}
public int getyCoor() {
    return yCoor;
}
public void setyCoor(int yCoor) {
    this.yCoor = yCoor;
}

}

Answer 1

好吧，所以问题归结为一些基本的数学......

如果我们看一下 BodyPart 的 draw 方法，您会发现...

g.fillRect(xCoor * width, yCoor * height, width, height);

好吧，非常基本，但是所有这些值实际上也都设置了吗？

如果我们看一下 tick 方法(在其中创建 BodyPart)，我们可以发现...

b = new BodyPart(xCoor, yCoor, 10);
snake.add(b);

好的，所以宽度和高度是10，但是xCoor和yCoor呢？

它们首先与类一起初始化为实例字段...

private int xCoor = 100, yCoor = 100, size = 10;

因此，简单的数学知识告诉我们 BodyPart 的初始位置是 100 * 10，等于 1000x1000。

如果我们也看一下...

public static final int WIDTH = 1000, HEIGHT = 1000; //Dimensions of the panel (Will be set by user input later)

和

setPreferredSize(new Dimension(WIDTH, HEIGHT));

我们可以看到 BodyPart 实际上最初是被设置在屏幕之外的。

所以，如果我们将初始位置更改为更像......

private int xCoor = 10, yCoor = 10, size = 10;

你会找到你失踪的蛇。

一般建议...

您应该避免重写paint。它在油漆链中的位置太高，很容易搞砸。相反，更喜欢使用 paintComponent (并确保您正在调用 super.paintComponent)。然后，JPanel 将为您清除Graphics 上下文(使用组件的背景颜色)。

Swing 不是线程安全的。您不应从事件调度线程的上下文外部修改 UI 或 UI 所依赖的任何状态。

当前的“主”循环存在引入脏更新的危险，这可能会在以后引起问题。请参阅Concurrency in Swing 。作为“一般”首选项，您应该考虑使用 Swing Timer反而。它不会阻止 EDT，但会在 EDT 内部生成“刻度”，从而使从内部更新 UI 和/或其状态更加安全。

执行操作时应避免使用“魔数(Magic Number)”...

for (int i = 0; i < WIDTH/10; i++) {
    g.drawLine(i*10, 0, i*10, HEIGHT);
}

此处，WIDTH 和 HEIGHT 可能并不代表组件的实际大小。请改用 JPanel#getWidth 和 JPanel#getHeight。

作为一般建议，您应该避免使用 setPreferred/Minimum/MaximumSize，其他人很容易将它们更改为您不想要的状态。相反，请重写 getPreferred/Minimum/MaximumSize，这样您就可以保持控制。