Java ArrayList 与 Arrays.asList() 返回的 List
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ArrayList vs the List returned by Arrays.asList()
提问by Roam
The method Arrays.asList(<T>...A)returns a Listrepresentation of A.
The returned object here is a Listbacked by an array, but is not an ArrayListobject.
该方法Arrays.asList(<T>...A)返回 的List表示A。这里返回的对象是一个List由数组支持的ArrayList对象，但不是一个对象。
I'm looking for the differences between the object Arrays.asList()returns and an ArrayListobject-- a quick source to tell these without diving into the code.
我正在寻找对象Arrays.asList()返回和对象之间的差异 -ArrayList一个快速来源，无需深入代码即可告诉这些。
TIA.
TIA。
采纳答案by SparkOn
When you call Arrays.asList it does not return a java.util.ArrayList. It returns a java.util.Arrays$ArrayListwhich is a fixed size list backed by the original source array. In other words, it is a view for the array exposed with Java's collection-based APIs.
当您调用 Arrays.asList 时，它不会返回java.util.ArrayList. 它返回一个java.util.Arrays$ArrayList由原始源数组支持的固定大小列表。换句话说，它是使用 Java 的基于集合的 API 公开的数组的视图。
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
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.
您不能向其中添加元素，也不能从中删除元素。如果您尝试在其中添加或删除元素，您将获得UnsupportedOperationException.
回答by Maroun
I'll expand my comment a little bit.
我会稍微扩展一下我的评论。
One problem that can occur if you use asListas it wasn't different from ArrayListobject:
如果您使用asList它，可能会出现一个问题，因为它与ArrayList对象没有区别：
List<Object> list = Array.asList(array) ;
list.remove(0); // UnsupportedOperationException :(
Here you cannot remove the 0 element because asListreturns a fixed-size list backed by the specified array. So you should do something like:
在这里您不能删除 0 元素，因为asList返回由指定数组支持的固定大小列表。所以你应该做这样的事情：
List<Object> newList = new ArrayList<>(Arrays.asList(array));
in order to make the newListmodifiable.
为了使newList可修改。
