在Java中实例化集合集？
问题描述：
我想实例化一组（字符串），然后将两个 Set< String> 放入其中，如下所示：
I want to instantiate a Set of Sets (of strings), and then place two Set<String>'s into it, like below:
Set<String> setOne = retrieveSetOne();
Set<String> setTwo = retrieveSetTwo();
Set<Set<String>> myCollection = new HashSet<new HashSet<String<()>(); // not working
myCollection.add(setOne);
myCollection.add(setTwo);
问题是，我对嵌套集的实例化不起作用。我该怎么做？
Problem is, my instantiation of the nested set does not work. How do I do this?
答
将其更改为
Set<Set<String>> myCollection = new HashSet<Set<String>>();
在创建实例时通过实现初始化，对于需要匹配声明的类型，
you initialize by implementation when you create instance, for type you need to match declaration,
如果您已经使用Java7，那么您只需使用
If you are on Java7 already then you can simply use
Set<Set<String>> myCollection = new HashSet<>();