java - 游戏显示空指针异常

Question

我试图显示一个黑色窗口，但我在第 72 行和第 43 行不断收到空指针异常。这是我的视频游戏的基础，自从我刚接触 java 以来，我一直在使用教程来帮助我。它开始时是一个无法访问的代码错误，但我通过返回修复了该错误，然后这个问题立即出现了任何帮助吗？代码:

package com.tyler99b.platformer.window;

import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;

public class Game extends Canvas implements Runnable
{

    private static final long serialVersionUID = 506346024107270629L;

    private boolean running = false;
    private Thread thread;

    public synchronized void start(){
        if(running)
            return;

        running = true;
        thread = new Thread(this);
        thread.start();
    }

    public void run()
    {
        long lastTime = System.nanoTime();
        double amountOfTicks = 60.0;
        double ns = 1000000000 / amountOfTicks;
        double delta = 0;
        long timer = System.currentTimeMillis();
        int updates = 0;
        int frames = 0;
        while(running){
            long now = System.nanoTime();
            delta += (now - lastTime) / ns;
            lastTime = now;
            while(delta >= 1){
                tick();
                updates++;
                delta--;
            }
            render();
            frames++;

            if(System.currentTimeMillis() - timer > 1000){
                timer += 1000;
                System.out.println("FPS: " + frames + " TICKS: " + updates);
                frames = 0;
                updates = 0;
            }
        }

    }

    private void tick()
    {

    }

    private void render()
    {


        BufferStrategy bs = this.getBufferStrategy();
        if(bs == null);
        {
            this.createBufferStrategy(3);

        }

        Graphics g = bs.getDrawGraphics();

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

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


    }

    public static void main(String args[]){
        new Window(800,600, "Platformer Prototype", new Game ());
    }
}

Answer 1

看来您正在使用一种常见的模式来创建空值。但是，在这里您将 bs 设置为 getBufferStrategy()，如果它为 null，则创建它。假设该功能成功。 bs 仍然为空

BufferStrategy bs = this.getBufferStrategy(); 
if (bs == null){
       this.createBufferStrategy(3); 
       //bs still null
}

您需要重新尝试将 bs 设置为等于某值

BufferStrategy bs = this.getBufferStrategy(); 
if (bs == null) {
       this.createBufferStrategy(3); 
       bs = this.getBufferStrategy(); 
}

所有这些都假设 createBufferStrategy 不会失败。如果可以的话，您必须决定在这种情况下该怎么做

其他说明

你的 if 语句也有一个停留；在里面。这使它成为一个空的 if 语句