java - 获取空对象引用但 ArrayList 已初始化

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 3 年前。

我的 ArrayList 已初始化，如下面的代码所示，但我仍然收到空对象引用错误。

String name;
int health;
int stamina;
int magic;
int strength;
Integer picture;
Integer croppedPicture;
static ArrayList<item> treasures = new ArrayList<>();

public item(String name, int health, int stamina, int magic, int strength, Integer picture, Integer croppedPicture, ArrayList<item> treasures){
    this.name = name;
    this.health = health;
    this.stamina = stamina;
    this.strength = strength;
    this.magic = magic;
    this.picture = picture;
    this.treasures = treasures;
    this.croppedPicture = croppedPicture;
}

static item[] adventurers = {new item("Forhum", 100, 5, 5, 20,R.drawable.forhum,R.drawable.forhum_cropped, treasures),
        new item("Triton", 100, 5, 5, 20,R.drawable.triton, R.drawable.triton_cropped, treasures),
        new item("Meravan", 100, 5, 5, 20,R.drawable.meravan, R.drawable.meravan_cropped, treasures)};

static item[] treasureList = {new item("Ring of Health", 10, 0, 0, 0, R.drawable.ring_of_health, null, null),
    new item("Ring of Stamina", 0, 5, 0,0, R.drawable.stam_green, null, null),
    new item("Ring of Strength", 0,0,0,5, R.drawable.ring_of_strength, null, null),
    new item("Cup of Magic", 0,0,4,0, R.drawable.cup_of_magic, null, null),
    new item("Invisible Necklace", 0,0,0,0, null, null, null),
    new item("Necklace of Harming", -10, 0,0,0, R.drawable.necklace, null, null)};

public String getName(){
    return name;
}

public int getHealth(){
    return health;
}

public int getMagic() {
    return magic;
}

public int getStamina() {
    return stamina;
}

public int getStrength() {
    return strength;
}

public ArrayList<item> getTreasures() {
    return treasures;
}

public void setHealth(int health) {
    this.health = health;
}

public void setMagic(int magic) {
    this.magic = magic;
}

public int getPicture() {
    return picture;
}

public void setTreasures(int treasure) {
    treasures.add(treasureList[treasure]);
}

public Integer getCroppedPicture() {
    return croppedPicture;
}

它使用此方法从战斗类获取 int:

    public void turn(){
       setText();
       if(monsterHealth > 0) {
          if (monsterMagic >= 5) {
            monsterUseMagic();
            setText();
          } else {
            monsterAttack();
            setText();
          }
          if(item.adventurers[personNumber].getHealth() > 0) {
            item.adventurers[personNumber].setMagic(item.adventurers[personNumber].getMagic() + 1);
            monsterMagic++;
            setText();
          }
          else{
            died();
          }
       }
       else {
          Intent won = new Intent(this, itemSelect.class);
          int treasure = rand.nextInt(6);
          int view = 2;
          won.putExtra("view", view);
          won.putExtra("thing", treasure);;
          item.adventurers[personNumber].setTreasures(treasure);
          startActivity(won);
       }
  }

这是我收到的错误。

2019-10-17 18:20:21.903 7907-7907/com.example.treasurehunt E/AndroidRuntime:致命异常:main

Process: com.example.treasurehunt, PID: 7907

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.util.ArrayList.add(java.lang.Object)' on a null object reference

    at com.example.treasurehunt.item.setTreasures(item.java:75)

    at com.example.treasurehunt.CombatScreen.turn(CombatScreen.java:118)

我正在制作的程序还有很多内容，但没有一个与此错误有关。感谢任何帮助。提前致谢。

Answer 1

尝试像下面这样初始化你的数组列表: static List<item> treasures = new ArrayList<>();

这就是我初始化 ArrayList 的方式，它的工作原理就像一个魅力。