当我尝试实例化包含2d接口数组的类时,我得到了NullPointerException。 在另一个类我有一个类型为CompetitionGround的对象,我尝试做这样的事情来初始化它:
CompetitionGround groud;
ground=new CompetitionGround(5);
我的类ArenaGround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();
}
全班是:
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Class Egg有两种类型的构造函数。我试过两个并得到同样的问题。我究竟做错了什么?我无法弄清楚。
答案 0 :(得分:1)
数组本身从未初始化,因此您无法为其元素分配任何内容。在初始化2嵌套for
循环之前,首先创建2D数组。
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();
}
答案 1 :(得分:0)
您无法初始化eggs
,这会导致您的问题。现在您正在初始化eggs
的每个元素,但如果您不首先初始化eggs
,那么这会给您带来问题。
我建议在构造函数中执行此操作:
public CompetitionGround(int boundries)
{
//Remember, you want IEgg, not Egg here
//This is so that you can add elements that implement IEgg but aren't Eggs
eggs = new IEgg[boundries][boundries];
for (int i = 0; i <boundries; i++)
{
for (int j = 0; j <boundries; j++)
{
eggs[i][j]=new Egg();
}
}
}
此外,这是无关的,但边界拼写错误。可能会在以后引起问题。