爲什麼我的BufferStrategy拋出一個NullpointerException，我該如何解決它？

Question

我一直在嘗試製作3D遊戲，出於某種原因，我的代碼正在拋出一個NullPointerException。我得到的錯誤是：

Exception in thread "Thread-3" 
java.lang.NullPointerException 
at Display_3d.render(Display_3d.java:73) 
at Display_3d.run(Display_3d.java:55) 
at java.lang.Thread.run(Unknown Source) 

該程序應該只顯示隨機顏色的像素作爲測試，以便以後製作3d圖形。還有兩個類使用，即使這兩個不扔錯誤，他們仍然可能是問題，所以我也會發布它們。類下面是拋出錯誤

import java.awt.Canvas; 
import javax.swing.JFrame; 
import java.awt.image.BufferedImage; 
import java.awt.image.BufferStrategy; 
import java.awt.image.DataBufferInt; 
import java.awt.Graphics; 

public class Display_3d extends Canvas implements Runnable { 
private static final long serialVersionUID = 1L; 

public static final int width = 800; 
public static final int height = 600; 
public static final String title = "Scott's Game Pre-Alpha 0.01"; 

private Thread thread; 
private Screen screen; 
private BufferedImage img; 
private boolean running = false; 
private Render render; 
private int[] pixels; 

public Display_3d(){ 
    Screen screen = new Screen(width,height); 
    img = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); 
    pixels = ((DataBufferInt)img.getRaster().getDataBuffer()).getData(); 
} 

private void start(){ 
    if (running){ 
    return; 
} 
running = true; 
Thread thread = new Thread(this); 
thread.start(); 

System.out.println("start() has been called sucessfully"); 
} 

private void stop(){ 
if (true != running){ 
    return; 
} 
running = false; 
try { 
    thread.join(); 
}catch (Exception e){ 
    e.printStackTrace(); 
    System.exit(0); 
} 
} 

public void run(){ 
    while (running){ 
    tick(); 
/*Line 55*/render(); 

} 
} 

private void tick(){ 

} 

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

    return; 
    } 


    /*Line 73*/ screen.render(); 

    for (int i = 0; i<width*height-1; i++){ 
    pixels[i] = screen.pixels[i]; 
    } 

    Graphics g = bs.getDrawGraphics(); 
    g.drawImage(img,0,0,width,height,null); 
    g.dispose(); 
    bs.show(); 
    } 


public static void main(String[] args){ 
Display_3d game = new Display_3d(); 
JFrame frame = new JFrame(); 
frame.add(game); 
frame.pack(); 
frame.setTitle(title); 
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 
frame.setSize(width,height); 
frame.setLocationRelativeTo(null); 
frame.setResizable(false); 
frame.setVisible(true); 

System.out.println("Running..."); 

game.start(); 

} 
} 

我呈現類的一個

public class Render{ 
    public final int width; 
    public final int height; 
    public final int[] pixels; 

    public Render (int width, int height){ 
    this.width = width; 
    this.height = height; 
    pixels = new int[width * height]; 
} 

public void draw(Render render, int xOffset, int yOffset){ 
    for (int y = 0; y<render.height; y++){ 
    int yPix = y + yOffset; 

    for (int x = 0; x<render.width; x++){ 
    int xPix = x + xOffset; 
    pixels[xPix + yPix * width] = render.pixels[x+y * render.width]; 

    } 
    } 
    } 
    public static void main (String[] args){} 
} 

我的屏幕類

import java.util.Random; 
public class Screen extends Render{ 
private Render test; 

public Screen(int width, int height){ 
    super(width,height); 
    Random random = new Random(); 
    test = new Render(256,256); 

    for (int i = 0; i <256*256; i++){ 
    test.pixels[i] = random.nextInt(); 
    } 
    } 

    public void render() { 
    draw(test,0,0); 
    } 

    public static void main (String[] args){} 
} 

Answer 1

在您coonstructor創建局部變量

public Display_3d(){ 
    Screen screen = new Screen(width,height); //<------------- 
    img = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); 
    pixels = ((DataBufferInt)img.getRaster().getDataBuffer()).getData(); 
} 

而是分配t Ø現場

public Display_3d(){ 
    this.screen = new Screen(width,height); //<------------- 
    img = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB); 
    pixels = ((DataBufferInt)img.getRaster().getDataBuffer()).getData(); 
} 

Answer 2

以下：

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

將創建一個「緩衝策略」，但它不會影響bs的價值，剛剛被證明是null。因此，您進一步使用bs的嘗試將會失敗。