java - 我在 Java 中遇到三个错误，但我不知道如何修复它们

Question

您好，我收到这些错误:

java.lang.IllegalArgumentException: input == null!
    at java.desktop/javax.imageio.ImageIO.read(ImageIO.java:1400)
    at com.game.main.BufferedImageLoader.loadImage(BufferedImageLoader.java:12)
    at com.game.main.Game.<init>(Game.java:48)
    at com.game.main.Game.main(Game.java:173)

BufferedImageLoader.java

package com.game.main;

import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;

public class BufferedImageLoader {

    BufferedImage image;

    public BufferedImage loadImage(String path) {
        try {
            image = ImageIO.read(getClass().getResource(path));
        } catch (Exception e) {
            e.printStackTrace();
        }
        return image;
    }
}

游戏.java

package com.game.main;
import java.awt.Canvas;
import java.awt.Color;
import java.awt.Graphics;
import java.awt.image.BufferStrategy;
import java.awt.image.BufferedImage;
import java.util.Random;

import javax.imageio.ImageIO;

public class Game extends Canvas implements Runnable{

    private static final long serialVersionUID = -473349850293143017L;

    public static final int WIDTH = 640, HEIGHT = WIDTH / 12 * 9;
    private Thread thread;
    private boolean running = false;

    public static boolean paused = false;
    public int diff = 0;

    // 0 = normal
    // 1 = hard

    private Random r;
    private Handler handler;
    private HUD hud;
    private Spawn spawner;
    private Menu menu;

    public enum STATE {
        Menu,
        Select,
        Help,
        Game,
        End
    };

    public static STATE gameState = STATE.Menu;

    public static BufferedImage sprite_sheet;

    public Game()  {

        BufferedImageLoader loader = new BufferedImageLoader();

        try {
            sprite_sheet = loader.loadImage("/JAVA-Game-Objects.png");
            System.out.print("loaded");
        } catch (Exception e) {
            e.printStackTrace();
        }
        handler = new Handler();
        hud = new HUD();
        menu = new Menu(this, handler, hud);
        this.addKeyListener(new KeyInput(handler, this));
        this.addMouseListener(menu);

        new Window(WIDTH, HEIGHT, "Game", this);

        spawner = new Spawn(handler, hud, this);
        r = new Random();

        if(gameState == STATE.Game) {
            handler.addObject(new Player(WIDTH/2-32, HEIGHT/2-32, ID.Player, handler));
            handler.addObject(new BasicEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
        } else {
            for (int i = 0; i < 20; i++) {
                handler.addObject(new MenuParticle(r.nextInt(WIDTH), r.nextInt(HEIGHT), ID.MenuParticle, handler));
            }
        }
    }
    public synchronized void start() {
        thread = new Thread(this);
        thread.start();
        running = true;
    }
    public synchronized void stop() {
        try {
            thread.join();
            running = false;
        } catch(Exception e) {
            e.printStackTrace();
        }
    }
    public void run() {
        this.requestFocus();
        long lastTime = System.nanoTime();
        double ns = 10000000;
        double delta = 0;
        long timer = System.currentTimeMillis();
        int frames = 0;
        while(running) {
            long now = System.nanoTime();
            delta +=  (now - lastTime) / ns;
            lastTime = now;
            while(delta >= 1) {
                tick();
                delta--;
            }
            if(running)
                render();
            frames++;

            if (System.currentTimeMillis() - timer > 1000) {
                timer += 1000;
                System.out.println("FPS: " + frames);
                frames = 0; 
            }
        }
        stop();
    }
    private void tick() {
        if (gameState == STATE.Game) {
            if (!paused) {
                handler.tick();
                hud.tick();
                spawner.tick();

                if (HUD.HEALTH <= 0) {
                    HUD.HEALTH = 100;
                    gameState = STATE.End;
                    handler.clearEnemies();
                    for (int i = 0; i < 20; i++) {
                        handler.addObject(new MenuParticle(r.nextInt(WIDTH), r.nextInt(HEIGHT), ID.MenuParticle, handler));
                    }
                }
            }

        } else if(gameState == STATE.Menu || gameState == STATE.End || gameState == STATE.Select) {
            menu.tick();
            handler.tick();
        }

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

        Graphics g = bs.getDrawGraphics();

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

        handler.render(g);

        if (paused) {
            g.setColor(Color.white);
            g.drawString("PAUSED", 100, 100);
        }

        if (gameState == STATE.Game) {
            hud.render(g);
        } else if(gameState == STATE.Menu || gameState == STATE.Help || gameState == STATE.End || gameState == STATE.Select) {
            menu.render(g);
        }
        g.dispose();
        bs.show();
    }
    public static float clamp(float y, float min, float max) {
        if (y >= max) {
            return y = max;
        } else if (y <= min) {
            return y = min;
        } else {
            return y;
        }
    }
    public static void main(String args[]) {
        new Game();
    }
}

第二个错误:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at com.game.main.SpriteSheet.grabImage(SpriteSheet.java:15)
    at com.game.main.Player.<init>(Player.java:21)
    at com.game.main.Menu.mousePressed(Menu.java:51)
    at java.desktop/java.awt.Component.processMouseEvent(Component.java:6633)
    at java.desktop/java.awt.Component.processEvent(Component.java:6401)
    at java.desktop/java.awt.Component.dispatchEventImpl(Component.java:5012)
    at java.desktop/java.awt.Component.dispatchEvent(Component.java:4844)
    at java.desktop/java.awt.EventQueue.dispatchEventImpl(EventQueue.java:772)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:721)
    at java.desktop/java.awt.EventQueue$4.run(EventQueue.java:715)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:95)
    at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:745)
    at java.desktop/java.awt.EventQueue$5.run(EventQueue.java:743)
    at java.base/java.security.AccessController.doPrivileged(AccessController.java:391)
    at java.base/java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:85)
    at java.desktop/java.awt.EventQueue.dispatchEvent(EventQueue.java:742)
    at java.desktop/java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:203)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:124)
    at java.desktop/java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:113)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:109)
    at java.desktop/java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
    at java.desktop/java.awt.EventDispatchThread.run(EventDispatchThread.java:90)

SpritheSheet.java

package com.game.main;

import java.awt.image.BufferedImage;

public class SpriteSheet {

    private BufferedImage sprite;


    public SpriteSheet(BufferedImage ss) {
        this.sprite = ss;
    }

    public BufferedImage grabImage(int col, int row, int width, int height) {
        BufferedImage img = sprite.getSubimage((row * 32) - 32, (col * 32) - 32, width, height);
        return img;
    }
}

Player.java

package com.game.main;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;

public class Player extends GameObject {

    Handler handler;

    private BufferedImage player_image;

    public Player(float x, float y, ID id, Handler handler) {
        super(x, y, id);
        this.handler = handler;

        SpriteSheet ss = new SpriteSheet(Game.sprite_sheet);

        player_image = ss.grabImage(1, 1, 32, 32);
    }
    public Rectangle getBounds() {
        return new Rectangle((int) x, (int) y, 32, 32);
    }
    public void tick() {
        x += velX;
        y += velY;

        x = Game.clamp(x, 0, Game.WIDTH - 50);
        y = Game.clamp(y, 0, Game.HEIGHT - 70);

        handler.addObject(new Trail(x, y, ID.Trail, Color.white, 32, 32, 0.05f, handler));


        collision();
    }

    private void collision() {
        for (int i = 0; i < handler.object.size(); i++) {

            GameObject tempObject = handler.object.get(i);

            if (tempObject.getId() == ID.BasicEnemy || tempObject.getId() == ID.FastEnemy || tempObject.getId() == ID.SmartEnemy) {
                if (getBounds().intersects(tempObject.getBounds())) {
                    HUD.HEALTH -= 2;
                }
            }
        }
    }
    public void render(Graphics g) {
        g.drawImage(player_image, (int) x, (int) y, null);
    }
}

菜单.java

package com.game.main;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.util.Random;

import com.game.main.Game.STATE;

public class Menu extends MouseAdapter{

    private Game game;
    private Handler handler;
    private HUD hud;

    Random r = new Random();

    public Menu(Game game, Handler handler, HUD hud) {
        this.game = game;
        this.hud = hud;
        this.handler = handler;
    }

    public void mousePressed(MouseEvent e) {
        int mx = e.getX();
        int my = e.getY();

        if(game.gameState == STATE.Menu) {
            // play
            if (mouseOver(mx, my, 210, 150, 200, 64)) {
                game.gameState = STATE.Select;
                return;
             }
            // help
            if (mouseOver(mx, my, 210, 250, 200, 64)) {
                game.gameState = STATE.Help;
            }

            // quit
            if (mouseOver(mx, my, 210, 350, 200, 64)) {
                System.exit(1);
            }
        }

        if(game.gameState == STATE.Select) {
            // normal
            if (mouseOver(mx, my, 210, 150, 200, 64)) {
                game.gameState = STATE.Game;
                handler.addObject(new Player(Game.WIDTH/2-32, Game.HEIGHT/2-32, ID.Player, handler));
                handler.clearEnemies();
                handler.addObject(new BasicEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));

                game.diff = 0;
             }
            // hard
            if (mouseOver(mx, my, 210, 250, 200, 64)) {
                game.gameState = STATE.Game;
                handler.addObject(new Player(Game.WIDTH/2-32, Game.HEIGHT/2-32, ID.Player, handler));
                handler.clearEnemies();
                handler.addObject(new HardEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));

                game.diff = 1;
            }

            // back
            if (mouseOver(mx, my, 210, 350, 200, 64)) {
                game.gameState = STATE.Menu;
                return;
            }
        }

        // back
        if (game.gameState == STATE.Help) {
            if (mouseOver(mx, my, 210, 350, 200, 64)) {
                game.gameState = STATE.Menu;
                return;
            }
        }
        // Try Again?
        if (game.gameState == STATE.End) {
            if (mouseOver(mx, my, 210, 350, 200, 64)) {
                game.gameState = STATE.Menu;
                hud.setLevel(1);
                hud.setScore(0);
            }
        }
    }
    public void mouseReleased(MouseEvent e) {

    }
    private boolean mouseOver(int mx, int my, int x, int y, int width, int height) {
        if (mx > x && mx < x + width) {
            if (my > y && my < y + height) {
                return true;
            } else return false;
        } else return false;
    }
    public void tick() {

    }
    public void render(Graphics g) {
        if (game.gameState == STATE.Menu) {
            Font fnt = new Font("arial", 1, 50);
            Font fnt2 = new Font("arial", 1, 30);

            g.setFont(fnt);
            g.setColor(Color.WHITE);
            g.drawString("Menu", 240, 50);


            g.setFont(fnt2);
            g.drawRect(210, 150, 200, 64);
            g.drawString("Play", 280, 190);

            g.drawRect(210, 250, 200, 64);
            g.drawString("Help", 280, 290);

            g.drawRect(210, 350, 200, 64);
            g.drawString("Quit", 280, 390);
        } else if (game.gameState == STATE.Help) {
            Font fnt = new Font("arial", 1, 50);
            Font fnt2 = new Font("arial", 1, 30);
            Font fnt3 = new Font("arial", 1, 20);

            g.setFont(fnt);
            g.setColor(Color.WHITE);
            g.drawString("Help", 240, 50);

            g.setFont(fnt3);
            g.drawString("Use WASD to move player and dodge enemies", 50, 200);

            g.setFont(fnt2);
            g.drawRect(210, 350, 200, 64);
            g.drawString("Back", 280, 390);
        } else if (game.gameState == STATE.End) {
            Font fnt = new Font("arial", 1, 50);
            Font fnt2 = new Font("arial", 1, 30);
            Font fnt3 = new Font("arial", 1, 20);

            g.setFont(fnt);
            g.setColor(Color.WHITE);
            g.drawString("Game Over", 180, 50);

            g.setFont(fnt3);
            g.drawString("You lost with a score of: " + hud.getScore() , 175, 200);

            g.setFont(fnt2);
            g.drawRect(210, 350, 200, 64);
            g.drawString("Try Again", 245, 390);
        } else if (game.gameState == STATE.Select) {
            Font fnt = new Font("arial", 1, 50);
            Font fnt2 = new Font("arial", 1, 30);

            g.setFont(fnt);
            g.setColor(Color.WHITE);
            g.drawString("SELECT DIFFICULTY", 140, 70);


            g.setFont(fnt2);
            g.drawRect(210, 150, 200, 64);
            g.drawString("Normal", 280, 190);

            g.drawRect(210, 250, 200, 64);
            g.drawString("Hard", 280, 290);

            g.drawRect(210, 350, 200, 64);
            g.drawString("Back", 280, 390);
        } 

    }
}

第三个错误:

Exception in thread "Thread-0" java.lang.NullPointerException
    at com.game.main.SpriteSheet.grabImage(SpriteSheet.java:15)
    at com.game.main.BasicEnemy.<init>(BasicEnemy.java:25)
    at com.game.main.Spawn.tick(Spawn.java:29)
    at com.game.main.Game.tick(Game.java:118)
    at com.game.main.Game.run(Game.java:98)
    at java.base/java.lang.Thread.run(Thread.java:830)

BasicEnemy.java

package com.game.main;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;

public class BasicEnemy extends GameObject{


    private Handler handler;

    private BufferedImage enemy_image;

    public BasicEnemy(float x, float y, ID id, Handler handler) {
        super(x, y, id);

        this.handler = handler;

        velX = 5;
        velY = 5;

        SpriteSheet ss = new SpriteSheet(Game.sprite_sheet);

        enemy_image = ss.grabImage(2, 1, 16, 16);
    }
    public Rectangle getBounds() {
        return new Rectangle((int)x, (int)y, 16, 16);
    }
    public void tick() {
        x += velX;
        y += velY;

        if (y <= 0 || y >= Game.HEIGHT - 54) velY *= -1;
        if (x <= 0 || x >= Game.WIDTH - 20) velX *= -1;

        //handler.addObject(new Trail(x, y, ID.Trail, Color.red, 16, 16, 0.02f, handler));
    }
    public void render(Graphics g) {
        g.drawImage(enemy_image, (int) x, (int) y, null);
    }
}

Spawn.java

package com.game.main;

import java.util.Random;

public class Spawn {

    private Handler handler;
    private HUD hud;
    private Game game;
    private Random r = new Random();

    private int scoreKeep = 0;

    public Spawn(Handler handler, HUD hud, Game game) {
        this.handler = handler;
        this.hud = hud;
        this.game = game;
    }

    public void tick() {
        scoreKeep++;

        if (scoreKeep >= 250) {
            scoreKeep = 0;
            hud.setLevel(hud.getLevel() + 1);

            if (game.diff == 0) {
                if (hud.getLevel() == 2) {
                    handler.addObject(new BasicEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
                } else if (hud.getLevel() == 3) {
                    handler.addObject(new BasicEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
                } else if (hud.getLevel() == 4) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 5) {
                    handler.addObject(new SmartEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.SmartEnemy, handler));
                } else if (hud.getLevel() == 6) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 7) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 10) {
                    handler.clearEnemies();
                    handler.addObject(new EnemyBoss((Game.WIDTH / 2) - 48, -120, ID.EnemyBoss, handler));
                }
            } else if (game.diff == 1) {
                if (hud.getLevel() == 2) {
                    handler.addObject(new HardEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
                } else if (hud.getLevel() == 3) {
                    handler.addObject(new HardEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.BasicEnemy, handler));
                } else if (hud.getLevel() == 4) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 5) {
                    handler.addObject(new SmartEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.SmartEnemy, handler));
                } else if (hud.getLevel() == 6) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 7) {
                    handler.addObject(new FastEnemy(r.nextInt(Game.WIDTH), r.nextInt(Game.HEIGHT), ID.FastEnemy, handler));
                } else if (hud.getLevel() == 10) {
                    handler.clearEnemies();
                    handler.addObject(new EnemyBoss((Game.WIDTH / 2) - 48, -120, ID.EnemyBoss, handler));
                }
            }
        }
    }
}

我不想在这里包含太多代码，所以如果您需要查看完整代码，这里有一个 GitHub 存储库:https://github.com/Super-Michael-05/Game-JAVA-Current-Project

我正在使用 Eclipse IDE。

如果您需要更多信息，请询问。

任何帮助都会有帮助。

Answer 1

对于第一个错误，放置文件路径而不是“路径”对我有用。因此，您可以尝试执行 image = ImageIO.read(getClass().getResources("/JAVA-Game-Objects.png"));。您还可以在此之前添加空检查，看看是否有帮助。

对于第二个和第三个错误，请尝试在“/JAVA-Game-Objects.png”前面添加“res”，以便得到 sprite_sheet = loader.loadImage("res/JAVA-Game-Objects.png") png”)；。我也在关注同一个系列，这就是为我修复这些错误的方法。