空指针异常array.length java [英] nullpointerexception array.length java

问题描述

每当我尝试访问我的阵列时，我都会收到 NPE.即使调用 .length 属性也会给我一个 NPE.任何帮助，将不胜感激.这是我的构造函数和不断失败的方法.

I've been getting an NPE whenever i try to access my array. Even calling for the .length attribute gives me an NPE. Any help would be appreciated. Here is my constructor and the method that keeps failing.

public SkierList() {
    Skier[] skiers= new Skier[INITIAL_CAP];
    for (int i = 0; i < skiers.length;i++){
        skiers[i] = new Skier("");
    }
    int count = 0;

}

public void add(Skier newSkier) {   
    if (this.size() < skiers.length)
    {
        skiers[count] = new Skier(newSkier.getName(), newSkier.getLevel());
        count++;
    }
}

代码编译但在skiers.length处抛出NPE

The code compiles but throws the NPE at skiers.length

推荐答案

您必须通过在构造函数中重新声明变量来隐藏变量.不要这样做，因为它会使字段为空.所以不是这个:

You must be shadowing the variable by redeclaring it in the constructor. Don't do that as it leaves the field null. So not this:

public class SkierList() {
    private Skier[] skiers; // this remains null

    public SkierList() {
        // you're re-declaring the skiers variable here
        // so only this local variable is non-null
        Skier[] skiers= new Skier[INITIAL_CAP];

        // ....
    }
}

而是

public class SkierList() {
    private Skier[] skiers; 

    public SkierList() {
        // Skier[] skiers= new Skier[INITIAL_CAP]; // Don't do this
        skiers = new Skier[INITIAL_CAP];  // note the difference
    }
}

或

public class SkierList() {
    private Skier[] skiers = new Skier[INITIAL_CAP];

    public SkierList() {
        // Skier[] skiers= new Skier[INITIAL_CAP];
    }
}

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