为什么在Set / List / Map中用于包装元素的方法的名称中包含'singleton'？（java.util.Collections）

Question

I know if I had element and I want to get List/Set/Map with eith element only I should invoke :

Collections.singleton() / Collections.singletonList() / Collections.singletonMap()

I don't understand why all these methods contains singleton in their names ?

I had assumption maybe it return same Collection for same object but this test shows that it is false

        Object o = new Object();
        System.out.println(Collections.singleton(o) == Collections.singleton(o));

output: false

For me singleton pattern forbid to create more than one element of concrete type and provided unify gateway for acces to this object.

please clarify.

Answer 1

It's a different meaning of the word "singleton" - it's not "the singleton pattern", it's "create a collection from a single item", that's all.

For example, from define:singleton :

a single person or thing of the kind under consideration.

Think of it this way: "singleton" is to "one thing" as "pair" is to "two things". So it wouldn't be entirely unnatural to have Collections.pair(T t1, T t2) in the same way.

Answer 2

这些方法背后的想法是，集合中的元素是一个单一的元素，而且将永远是-你不能从集合中删除它，也不能添加其他项目到这个集合。