Arrays.asList（）vs Collections.singletonList（） [英] Arrays.asList() vs Collections.singletonList()

问题描述

使用Arrays.asList（something）而不是Collections.singletonList（something）来创建一个包含一个项目的列表有一个优点（或许多差别）？

Collections.singletonList（something）是 immutable ，而 Arrays.asList（something）是固定大小 List 数组的表示，其中列表和数组在堆中连接。

Arrays.asList（something）允许对其进行非结构更改它被反映到List和联合数组。它会添加 UnsupportedOperationException ，虽然您可以为特定索引设置元素。

对 Collections.singletonList（something）返回的列表所做的任何更改将导致 UnsupportedOperationException 。

此外， Collections.singletonList（something）返回的List的容量总是 1 c> Arrays.asList（something），其容量将是所支持数组的大小。

Is there an advantage (or much of a difference) to using Arrays.asList(something) over Collections.singletonList(something) to make a list containing one item? The latter makes the returned list immutable as well.

解决方案

Collections.singletonList(something) is immutable whereas Arrays.asList(something) is a fixed size List representation of an Array where the List and Array gets joined in the heap.

Arrays.asList(something) allows non-structural changes made to it, which gets reflected to both the List and the conjoined array. It throws UnsupportedOperationException for adding, removing elements although you can set an element for a particular index.

Any changes made to the List returned by Collections.singletonList(something) will result in UnsupportedOperationException.

Also, the capacity of the List returned by Collections.singletonList(something) will always be 1 unlike Arrays.asList(something) whose capacity will be the size of the backed array.

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