Java 2 NPE错误

Question

我正在测试我的游戏，然后突然出现2个随机的NullPointerExceptions！一个是在我的勾选线程上，一个是在尝试在默认线程上播放音乐时。这是错误：

Exception in thread "Thread-2" java.lang.NullPointerException
    at com.darkbyte.games.tfa.game.world.room.RoomManager.tick(RoomManager.java:29)
    at com.darkbyte.games.tfa.game.world.WorldManager.tick(WorldManager.java:73)
    at com.darkbyte.games.tfa.game.GameManager.tick(GameManager.java:27)
    at com.darkbyte.games.tfa.screens.Game.tick(Game.java:24)
    at com.darkbyte.games.tfa.screens.ScreenManager.tickScreen(ScreenManager.java:72)
    at com.darkbyte.games.tfa.tick.TickManager.tick(TickManager.java:54)
    at com.darkbyte.games.tfa.tick.TickManager.run(TickManager.java:87)
    at java.lang.Thread.run(Unknown Source)
Exception in thread "LWJGL Application" java.lang.NullPointerException
    at com.darkbyte.games.tfa.game.world.WorldManager.render(WorldManager.java:61)
    at com.darkbyte.games.tfa.game.GameManager.render(GameManager.java:22)
    at com.darkbyte.games.tfa.screens.Game.render(Game.java:19)
    at com.darkbyte.games.tfa.screens.ScreenManager.renderScreen(ScreenManager.java:44)
    at com.darkbyte.games.tfa.render.RenderManager.render(RenderManager.java:54)
    at com.darkbyte.games.tfa.Core.render(Core.java:55)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:215)
    at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:120)

以下是所涉及的课程，大约有50个，所以如果您想再看到它们，请发表评论，我可以提供链接：

RoomManager：

package com.darkbyte.games.tfa.game.world.room;

public class RoomManager {

    //Stores the current room
    private static Room currentRoom;

    //Initialises the rooms
    public static void init() {
        //Loops through the rooms in the enumerator and initialises them
        for(Rooms roomEnum : Rooms.values()) roomEnum.getRoom().init();
        //Sets the current room to a test room (For test builds only, will be updated with alpha+ releases when saving is implemented)
        currentRoom = Rooms.TEST_ROOM.getRoom();
    }

    //Disposes of the rooms
    public static void dispose() {
        //Loops through the rooms in the enumerator and disposes of them
        for(Rooms roomEnum : Rooms.values()) roomEnum.getRoom().dispose();
    }

    //Renders the current room
    public static void render() {
        currentRoom.render();
    }

    //Runs the tick code for the current room
    public static void tick() {
        currentRoom.tick();
    }

    //Returns the current room
    public static Room getCurrentRoom() {
        return currentRoom;
    }

    //Sets the current room
    public static void setCurrentRoom(Room currentRoom) {
        RoomManager.currentRoom = currentRoom;
    }
}

间：

package com.darkbyte.games.tfa.game.world.room;

import java.util.ArrayList;

import com.badlogic.gdx.maps.tiled.TiledMap;
import com.badlogic.gdx.maps.tiled.renderers.OrthogonalTiledMapRenderer;
import com.darkbyte.games.tfa.game.entity.Entity;

public abstract class Room {

    //The room's name
    protected String roomName;
    //Stores all the entities in the current room
    protected ArrayList<Entity> entitiesInRoom = new ArrayList<Entity>();
    //The tile map for the room
    protected TiledMap tileMap;
    //The map renderer for the room
    protected OrthogonalTiledMapRenderer mapRenderer;

    //Returns all the entities in the current room
    public ArrayList<Entity> getEntities() {
        return entitiesInRoom;
    }

    //Sets the entities in the room
    public void setEntities(ArrayList<Entity> entities) {
        entitiesInRoom = entities;
    }

    //The initialisation method for the room
    public abstract void init();

    //The disposal method for the room
    public abstract void dispose();

    //The render method for the room
    public abstract void render();

    //The tick method for the room
    public abstract void tick();
}

房间：

package com.darkbyte.games.tfa.game.world.room;

import com.badlogic.gdx.assets.loaders.resolvers.LocalFileHandleResolver;
import com.badlogic.gdx.maps.tiled.TiledMap;
import com.badlogic.gdx.maps.tiled.TmxMapLoader;
import com.darkbyte.games.tfa.game.world.room.rooms.TestRoom;

public enum Rooms {
    //A list of all the rooms in the game
    TEST_ROOM(new TestRoom());

    //The constructor for the rooms
    Rooms(Room room) {
        this.room = room;
    }

    //Stores the room
    private Room room;
    //The file handle resolver to allow the maps to be loaded from local folders
    private static LocalFileHandleResolver handleResolver = new LocalFileHandleResolver();
    //The map loader for the rooms
    private static TmxMapLoader mapLoader = new TmxMapLoader(handleResolver);

    //A getter to get the room it represents
    public Room getRoom() {
        return room;
    }

    //Gets a map using the map loader and handle resolver
    public static TiledMap generateMap(String location) {
        return mapLoader.load(location);
    }
}

WorldManager：

package com.darkbyte.games.tfa.game.world;

import java.io.File;
import java.util.Random;

import com.badlogic.gdx.Gdx;
import com.badlogic.gdx.audio.Music;
import com.darkbyte.games.tfa.game.world.room.RoomManager;

public class WorldManager {

    //The array of music that can be played in the world
    private static Music[] ambienceTracks;
    //The object to store the currently playing music
    private static Music currentTrack;
    //The object to choose a track from the list randomly, it is seeded by the system's nano time
    private static Random musicPicker = new Random(System.nanoTime());

    //Initialises the world
    public static void init() {
        //Gets the folder that stores the ambience music and creates a File object of it
        File[] ambienceFolder = new File("assets/world/ambience").listFiles();
        //Gets the amount of tracks in the folder then creates an array using that amount
        ambienceTracks = new Music[ambienceFolder.length];
        //A variable to store the number of files added to the ambience tracks
        int tracksFound = 0;

        //Loops through the files in the folder and creates an instance of it in the form of a Music object
        for(int i = 0; i < ambienceFolder.length; i++) {
            //Checks if the file is a valid music file that is supported by the library
            if(ambienceFolder[i].getName().endsWith(".ogg") || ambienceFolder[i].getName().endsWith(".mp3") || ambienceFolder[i].getName().endsWith(".wav")) {
                //Generates an element of the array using the file found
                ambienceTracks[tracksFound] = Gdx.audio.newMusic(Gdx.files.local("assets/world/ambience/" + ambienceFolder[i].getName()));
                //Increments the tracks found
                tracksFound++;
            }
        }

        //Initialises the room manager
        RoomManager.init();
    }

    //Disposes of the world
    public static void dispose() {
        //Loops through the ambience and disposes of it
        for(Music ambienceTrack : ambienceTracks) ambienceTrack.dispose();
        //Disposes of the room manager
        RoomManager.dispose();
    }

    //Renders the world
    public static void render() {
        //Checks if the current track is null to avoid NPE errors
        if(currentTrack != null) {
            //Checks to see if the current track has ended
            if(!currentTrack.isPlaying()) {
                //Chooses a new track at random if it has ended
                currentTrack = ambienceTracks[musicPicker.nextInt(ambienceTracks.length)];
            }
            //If the current track is null, it chooses a new track at random
        } else currentTrack = ambienceTracks[musicPicker.nextInt(ambienceTracks.length)];

        //Plays the current track
        currentTrack.play();

        //Renders the current room
        RoomManager.render();
    }

    //Runs the tick code for the world
    public static void tick() {
        //Runs the tick code for the current room
        RoomManager.tick();
    }
}

Answer 1

很难找到NPE的原因，因为我们没有完整的来源。

在调用WorldManager.init()和RoomManager.tick()之前，似乎未调用WorldManager.render()。您应该在WorldManager.init()中放置一个断点来测试是否在崩溃之前调用了它。

Answer 2

我解决了它，它没有进入另一个类的主init()方法。我确实设法使我的一些代码更有效率，所以我想最终会有一些好的结果：）