为什么Collections.frequency在转换列表上没有按预期工作？ [英] Why is Collections.frequency not working as expected on converted list?

问题描述

我过去使用过Collections.frequency并且工作正常，但我现在遇到问题，因为我正在使用int []。

I have used Collections.frequency in the past and its worked fine but I'm having problems now that I'm using an int[].

基本上是收藏.frequency需要一个数组，但我的数据是int []的形式，所以我转换我的列表，但没有得到结果。我认为我的错误在于转换列表但不确定如何操作。

Basically Collections.frequency requires a array but my data is in the form of a int[] so I convert my list but am not getting an results. I think my mistake is in the converting of the list but not sure how to do it.

以下是我的问题示例：

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;

public class stackexample {
    public static void main(String[] args) {
        int[] data = new int[] { 5,0, 0, 1};
        int occurrences = Collections.frequency(Arrays.asList(data), 0);
        System.out.println("occurrences of zero is " + occurrences); //shows 0 but answer should be 2
    }
}

我不知道得到一个错误只是零，但当我尝试列出 Arrays.asList（data）中的项目时，我得到了奇怪的数据，如果我只是直接添加数据，它想要将我的列表转换为集合<？>

I don't get an error just zero but I get weird data when I try to list the items in Arrays.asList(data), if I just add data directly, it wants to convert my list into collections<?>

有任何建议吗？

推荐答案

这有效：

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class stackexample {
    public static void main(String[] args) {
        List<Integer> values = Arrays.asList( 5, 0, 0, 2 );
        int occurrences = Collections.frequency(values, 0);
        System.out.println("occurrences of zero is " + occurrences); //shows 0 but answer should be 2
    }
}

这是因为 Arrays.asList 没有给出你的想法：

It's because Arrays.asList isn't giving you what you think it is:

http://mlangc.wordpress.com/2010/05/ 01 / be-carefull-when-converting-java-arrays-to-lists /

您将获得列表 int [] ，而非 int 。

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