如何修复 try/catch Java NullPointerException

Question

我正在尝试按照 this 教程创建 2D 平台游戏。我创建了一个 Images()-class ，如下所示：包资源；

import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Objects;

public class Images {

    public static BufferedImage[] tileBlocks;

    public Images(){
        tileBlocks = new BufferedImage[1];
        try{
            tileBlocks[0] = ImageIO.read(
                    // TODO: Fix the error caused by this try/catch
                    (Objects.requireNonNull(getClass().getResourceAsStream("TileBlocks/block_brick.png")))
            );
        } catch (IOException e) { e.printStackTrace(); }
    }
}

我在 GamePanel()-class 中创建了它的实例，看起来像这样

package Main;

import GameState.GameStateManager;
import Resources.Images;

import javax.swing.*;
import java.awt.*;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.io.Serial;

@SuppressWarnings("BusyWait")
public class GamePanel extends JPanel implements Runnable, KeyListener {

    @Serial
    private static final long serialVersionUID = 1L;

    // Game thread
    private boolean isRunning = false;
    int FPS = 60;                                       // Frames per second
    long targetTime = 1000 / FPS;                       // Set target time

    // Set the dimension of the game-window
    public static final int WIDTH = 800;
    public static final int HEIGHT = 600;

    private GameStateManager gsm = new GameStateManager(); // Game state manager object

    public GamePanel(){
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        addKeyListener(this);
        setFocusable(true);

        // TODO: Fix error (Reports instantiation of utility classes using the new keyword)
        new Images();

        start();
    }

    // Start the game (initialize)
    private void start() {
        isRunning = true;
        Thread thread = new Thread(this);            // Referring to Runnable
        thread.start();                              // Call to our game-loop
    }

    // Game-loop
    public void run() {

        long start, elapsed, wait;                          // Keep track of time
        gsm = new GameStateManager();                       // Initialize game state manager

        while (isRunning) {
            start = System.nanoTime(); // Start timer
            update();                  // Update the game-logic
            repaint();                 // Re-paint the board (built-in method from java.awt)
            elapsed = System.nanoTime() - start;

            // If everything runs in under the target time we wait (so it runs equally in all computers)
            wait = targetTime - elapsed / 1000000;  // Divide by 1 000 000 to get milli-seconds
            if (wait <= 0) { wait = 5; }  // Keep wait a positive value

            try {
                Thread.sleep(wait);
            } catch (Exception e) { e.printStackTrace(); } 
        }
    }

    // Updating all game-logic
    public void update() { gsm.update(); }// Call methods from game state manager in the game panel class

    // Where we draw the graphics
    public void paintComponent(Graphics g){
        super.paintComponent(g);         // Built-in method from java.awt
        g.clearRect(0,0,WIDTH,HEIGHT);   // Clear the screen before drawing
        gsm.draw(g);                     // Call method from game state manager in the game panel class
    }

    public void keyPressed(KeyEvent e) {
        gsm.keyPressed(e.getKeyCode());  // getKeyCode() turns KeyEvent into an integer
    }

    public void keyReleased(KeyEvent e) {
        gsm.keyReleased(e.getKeyCode()); // getKeyCode() turns KeyEvent into an integer
    }

    public void keyTyped(KeyEvent e) { }
}

我收到一条错误消息

Instantiation of utility class 'Images' 
Inspection info: Reports instantiation of utility classes using the new keyword.
In utility classes, all fields and methods are static. 
Instantiation of such classes is most likely unnecessary and indicates a mistake.

当我尝试运行游戏时，它没有启动，我只得到 NullPointerException

Exception in thread "main" java.lang.NullPointerException
    at java.base/java.util.Objects.requireNonNull(Objects.java:208)
    at inf112.skeleton.app/Resources.Images.<init>(Images.java:17)
    at inf112.skeleton.app/Main.GamePanel.<init>(GamePanel.java:35)
    at inf112.skeleton.app/Main.Game.game(Game.java:10)
    at inf112.skeleton.app/Main.Game.main(Game.java:20)

但如果我删除实例化，游戏会启动，但随后会崩溃并出现更多错误

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: 
Cannot load from object array because "Resources.Images.tileBlocks" is null
etc...

如果我从中删除 Objects.requireNonNull tileBlocks[0] = ImageIO.read((getClass().getResourceAsStream("TileBlocks/block_brick.png"))

游戏启动，但它崩溃了，我收到另一个错误提示

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException: 
Cannot load from object array because "Resources.Images.tileBlocks" is null

我在这里做错了什么？为什么我的列表是tileBlocks null？如何读取图像并将其显示在 tileBlocks 上？

Answer 1

将文件“block_brick.png”放入类路径中的目录“TileBlocks”中。

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