java - 在java中初始化自定义类的二维数组

Question

当我尝试实例化包含二维接口(interface)数组的类时，出现 NullPointerException。在另一个类中，我有一个CompetitionGround类型的对象，我尝试做这样的事情来初始化它:

CompetitionGround groud;
ground=new CompetitionGround(5);

我的 ComparisonGround 类的构造函数如下所示:

public CompetitionGround(int boundries) {
    for (int i = 0; i <boundries; i++)
        for (int j = 0; j <boundries; j++)
            eggs[i][j]=new Egg();
}

全类是:

public class CompetitionGround {

    private IEgg eggs[][];

    public void goIn(Rabbit rabbit) {
        IPozition temp = rabbit.getPozition();
        rabbit.Collect(eggs[temp.getPozitionX()][temp.getPozitionY()]);
    }

    public CompetitionGround(int boundries) {
        for (int i = 0; i < boundries; i++)
            for (int j = 0; j < boundries; j++)
                eggs[i][j] = new Egg();
    }

    public void AddEgg(int x, int y, int points) {
        eggs[x][y] = new Egg(points);
    }
}

实现 IEgg 的 Egg 类有两种类型的构造函数。我尝试了两者并遇到了同样的问题。我究竟做错了什么？我想不通。

Answer 1

数组本身从未初始化，因此您还不能为其元素分配任何内容。在 2 个嵌套 for 循环中初始化之前，首先创建 2D 数组本身。

public CompetitionGround(int boundries  /* [sic] */) {
    // Init array here.
    eggs = new IEgg[boundries][boundries];

    // You should use proper indenting.
    for (int i = 0; i < boundries; i++)
       for (int j = 0; j < boundries; j++)
           eggs[i][j] = new Egg();
}