如何在 Java 中从数组 (int[]) 创建 ArrayList (ArrayList<Integer>) [英] How to create ArrayList (ArrayList&lt;Integer&gt;) from array (int[]) in Java

问题描述

我看到了这个问题:从数组创建 ArrayList

但是，当我使用以下代码尝试该解决方案时，它并不能在所有情况下都有效:

However when I try that solution with following code, it doesn't quite work in all the cases:

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.List;

public class ToArrayList {

    public static void main(String[] args) {
        // this works
        String[] elements = new String[] { "Ryan", "Julie", "Bob" };
        List<String> list = new ArrayList<String>(Arrays.asList(elements));
        System.out.println(list);

        // this works
        List<Integer> intList = null;
        intList = Arrays.asList(3, 5);
        System.out.println(intList);

        int[] intArray = new int[] { 0, 1 };
        // this doesn't work!
        intList = new ArrayList<Integer>(Arrays.asList(intArray));
        System.out.println(intList);
    }
}

我在这里做错了什么?代码不应该intList = new ArrayList(Arrays.asList(intArray)); 编译就好了吗?

What am I doing wrong here? Shouldn't the code intList = new ArrayList<Integer>(Arrays.asList(intArray)); compile just fine?

推荐答案

问题在

intList = new ArrayList<Integer>(Arrays.asList(intArray));

是 int[] 被视为单个 Object 实例，因为原始数组从 Object 扩展.如果您使用 Integer[] 而不是 int[] 这将起作用，因为现在您正在发送一个 Object 数组.

is that int[] is considered as a single Object instance since a primitive array extends from Object. This would work if you have Integer[] instead of int[] since now you're sending an array of Object.

Integer[] intArray = new Integer[] { 0, 1 };
//now you're sending a Object array
intList = new ArrayList<Integer>(Arrays.asList(intArray));

根据您的评论:如果您仍想使用 int[](或其他原始类型数组)作为主数据，则需要使用包装类创建一个额外的数组.对于这个例子:

From your comment: if you want to still use an int[] (or another primitive type array) as main data, then you need to create an additional array with the wrapper class. For this example:

int[] intArray = new int[] { 0, 1 };
Integer[] integerArray = new Integer[intArray.length];
int i = 0;
for(int intValue : intArray) {
    integerArray[i++] = intValue;
}
intList = new ArrayList<Integer>(Arrays.asList(integerArray));

但是由于您已经在使用 for 循环，我不介意使用临时包装类数组，只需将您的项目直接添加到列表中即可:

But since you're already using a for loop, I wouldn't mind using a temp wrapper class array, just add your items directly into the list:

int[] intArray = new int[] { 0, 1 };
intList = new ArrayList<Integer>();
for(int intValue : intArray) {
    intList.add(intValue);
}

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