ArrayList 与 Arrays.asList() 返回的 List [英] ArrayList vs the List returned by Arrays.asList()

问题描述

方法Arrays.asList(...A) 返回一个 List 表示 A.这里返回的对象是一个 List 由数组支持，但不是 ArrayList 对象.

The method Arrays.asList(<T>...A) returns a List representation of A. The returned object here is a List backed by an array, but is not an ArrayList object.

我正在寻找对象之间的差异 Arrays.asList() 返回和一个 ArrayList 对象——无需深入代码即可快速了解这些信息的来源.

I'm looking for the differences between the object Arrays.asList() returns and an ArrayList object-- a quick source to tell these without diving into the code.

TIA.

推荐答案

当您调用 Arrays.asList 时，它不会返回 java.util.ArrayList.它返回一个 java.util.Arrays$ArrayList，它是一个由原始源数组支持的固定大小的列表.换句话说，它是使用 Java 的基于集合的 API 公开的数组的视图.

When you call Arrays.asList it does not return a java.util.ArrayList. It returns a java.util.Arrays$ArrayList which is a fixed size list backed by the original source array. In other words, it is a view for the array exposed with Java's collection-based APIs.

    String[] sourceArr = {"A", "B", "C"};
    List<String> list = Arrays.asList(sourceArr);
    System.out.println(list); // [A, B, C]

    sourceArr[2] = ""; // changing source array changes the exposed view List
    System.out.println(list); //[A, B, ]

    list.set(0, "Z"); // Setting an element within the size of the source array
    System.out.println(Arrays.toString(sourceArr)); //[Z, B, ]

    list.set(3, "Z"); // java.lang.ArrayIndexOutOfBoundsException
    System.out.println(Arrays.toString(sourceArr));

    list.add("X"); //java.lang.UnsupportedOperationException

    list.remove("Z"); //java.lang.UnsupportedOperationException

您不能向其中添加元素，也不能从中删除元素.如果您尝试向其中添加或删除元素，您将收到 UnsupportedOperationException.

You cannot add elements to it and you cannot remove elements from it. If you try to add or remove elements from them you will get UnsupportedOperationException.

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