java数组nullpointer [英] java array nullpointer

问题描述

我正在尝试查找数组的最小值.该数组包含Nodes-一个包含元素E和优先级int的节点.我想在阵列中找到优先级最低的节点.

I'm trying to find minimum of an array. The array contain Nodes - a node contains of an element E and a priority int. Im want to find the Node in the array with the smallest priority.

@Override
public E min() {
    Node temp = S[0];
    for(int i = 1; i<S.length; i++){
        int prio= S[i].getPrioritet();   <-- nullpointer excp.
        if(prio<temp.getPrioritet()){
            temp = S[i];
        }
    }
    return temp.getElement();

但是当我尝试使用它时，我得到了一个nullpointer异常.有人知道我在做什么错吗?

But i get an nullpointer exception when i try to use it. Does anybody know what im doing wrong?

这是我的考试:

PrioritetArraySorteret<String> p = new PrioritetArraySorteret<String>();

    p.insert(1, "Hello");
    p.insert(3, "Hi");
    p.insert(4, "Hawdy");
    System.out.println(p.min());

}

推荐答案

这仅表示数组 S 的索引之一处的元素为空.也许您以 n 的大小初始化了数组，但填充的位置少于 n 个位置.

It simply means that the element at one of the indexes of array S is null. Maybe you're initialized the array at a size n but filled in less than n positions.

这样修改可能会解决此问题:

Altering like this will probably fix it:

for(int i = 1; i<S.length; i++){
    if(S[i] != null) {
        int prio= S[i].getPrioritet();   <-- nullpointer excp.
        if(prio<temp.getPrioritet()){
            temp = S[i];
        }
     }
}

也就是说，您可能在这里重新发明了轮子.使用一个简单的 ArrayList 参数化为您定义的某种类型，该类型封装了一个值和优先级.然后，您可以使用具有优先级的 compareTo 方法让该类型实现 Comparable ，或者编写一个 Comparator 来查找最小值:

That said, you might be reinventing the wheel here a bit. Using a simple ArrayList parameterized with some type that you define which encapsulates a value and priority would do. You could then have that type implement Comparable with a compareTo method that uses the priority, or write a Comparator to use for finding the minimum:

List<YourType<String>> list = new ArrayList<YourType<String>>();
Collections.min(list);

或者，如果您使用的是自定义比较器:

Or, if you're using a custom Comparator:

Collections.min(list, yourComparator);

-编辑了 min ，而不是 sort .抱歉.

-- edited for min instead of sort. Sorry.

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