Question

这段代码有什么问题？
我一直收到错误

Exception in thread "Thread-2" java.lang.NullPointerException 
at GUI.render(GUI.java:68) 
at GUI.run(GUI.java:51)

请帮助

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

public class GUI extends Canvas implements Runnable {
    private static final long serialVersionUID = 1L;
    final static String LABEL_TEXT = "Game";
    public static final int Width = 1020;
    public static final int Height = 680;
    private Thread thread;
    private Screen screen;
    private Render render;
    private BufferedImage img;
    private boolean running = false;
    private int[] pixels;

    public void display() {
        screen = new Screen(Height, Width);
    vimg = new BufferedImage(Width, Height, BufferedImage.TYPE_INT_RGB);
    pixels = ((DataBufferInt)img.getRaster().getDataBuffer()).getData();
    }

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

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

    public void run() {
        while (running){
            tick();
            render();
        }
    }

    public void tick() {

    }

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

        screen.render();

        for (int i = 0; i <Width*Height; i++){
             pixels[i] = screen.pixels[i];
        }
        Graphics g = bs.getDrawGraphics();
        g.drawImage(img, 0, 0, Width, Height, null);
        g.dispose();
        bs.show();
    }


    /**
     * Create and show the GUI.
     */
    public static void main(String[] args) {
        /*Create Canvas*/
        GUI game = new GUI();

        /*Create and set up the frame*/
        JFrame frame = new JFrame("GUI");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        /*Add content pane to frame*/
        frame.add(game);

        /*Size and then display the frame.*/
        frame.setSize(Width, Height);
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);

        game.start();
    }
 }

 package graphics;

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

    public Render(int height, int width) {
        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<height; y++) {
            int yPix = y + yOffset;
            for (int x =0; x<width; x++) {
                int xPix = x + xOffset;

                pixels[xPix+yPix*width] =  pixels[x+y*width];
            }
        }
    }
 }


package graphics;

import java.util.Random;
import graphics.Render;

public class Screen extends Render{

    private Render test;

    public Screen(int width, int height) {
        super(width, height);
        Random rand = new Random();
        test = new Render(256, 256);
        for (int i =0; i< 256*256; i++){
            test.pixels[i] = rand.nextInt();
        }
    }

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

Answer 1

在使用变量之前，您尚未调用display()来初始化变量。

NullPointerException - 我不明白

1 个答案: