Question

我正在尝试使用lwjgl / Java制作游戏，但是当涉及到关卡创建时，我在尝试将我的实体放入ArrayList时遇到了多个问题。我稍后将在txt文件中创建级别，而我会将它们存储在那里，但是现在这是我唯一的选择。当我尝试运行游戏时，我得到一个NullPointerException。

public class Level {

int levels = 10;

Player player;

@SuppressWarnings("unchecked")
ArrayList<Entity>[] entities = (ArrayList<Entity>[]) new ArrayList[50];
Enemy[] enemies = new Enemy[20];        //This it later going to be added in the entities arrayList
                        //The reason its a normal array is so that it would work with collision detection



//Pre-init of the levels should be done here
public Level(){

    player = new Player(90, 40);

    for(int i = 0; i <= levels; i++)
    createLevels(i);
}

//Collision check
public void update(){
    //Checking collision against enemies
    for(int i = 0; i <= levels; i++ ){
    Utilities.util.isColliding(player, enemies[i]);
    }
}


/*  LEVEL CREATION
 * 
 * The first thing that is going to be in the "level editor" text file
 * is which level the items are going to be added to. Like so:
 *      - level 0
 * 
 * The entity adding is later going to be added in a text file as so:
 *      - Group entity xPos yPos Width Height
 *      - enemies enemy 60 60, 200, 100
 * 
 * The player postition is the first two numbers in txt file,
 * Player is also the last item that should be added to entities
 */

public void createLevels(int level){

    System.out.println("Level " + level + " is being created.");

    if(level == 0){


        addEntity(player, level);

        addEnemy(new Wall(40, 40, 200, 322), level);


        //Adding all enemies to entities
        for(int i = 0; i <= enemies.length; i++){
        entities[level].add(enemies[i]);
        }
    }

    System.out.println("Level " + level + " was created!");

}

private void addEntity(Entity ent, int level){
    entities[level].add(ent);
}

private void addEnemy(Enemy nmy, int level){
    enemies[level] = nmy;
}

我已经有这个问题很长一段时间了，我很想得到一些帮助。我知道这可能是一个非常无聊的问题，但请帮助我！

这是NullPointerException

Exception in thread "main" java.lang.NullPointerException
at com.sontvedt.engine.Level.addEntity(Level.java:119)
at com.sontvedt.engine.Level.createLevels(Level.java:59)
at com.sontvedt.engine.Level.<init>(Level.java:27)
at com.sontvedt.engine.Game.<init>(Game.java:14)
at com.sontvedt.engine.Window.initGame(Window.java:42)
at com.sontvedt.engine.Window.init(Window.java:36)
at com.sontvedt.engine.Window.main(Window.java:24)

第119行是addEntity方法创建

Answer 1

异常发生在以下行：

entities[level].add(ent);

因此，entities为空，或entities[level]为空。

entities不能为空，因为它已在此处初始化：

ArrayList<Entity>[] entities = (ArrayList<Entity>[]) new ArrayList[50];

因此，唯一可能的原因是entities[level]为空。代码中是否存在创建新ArrayList并存储在entities数组中的某个位置？我找不到任何。

级别创建和ArrayList问题

1 个答案: