java - 怎么把四个list集合整合到一个集合中。

Question

把四个集合里面的内容都存入一个集合（最后的集合已经有了四个集合的set，get方法了）

怎么四变一

Answer 1

addAll() doesn’t work...

Answer 2

Are the generics of these four collections the same?

Answer 3

If the generics are consistent, use the addall() method to add it to a new List. If you need to remove duplicates, use Set’s addall ()

Answer 4

Write a wrapper collection class and delegate to the corresponding sub-collection as needed.
Usually just inherit AbstractList, and the constructor puts four or more sub-collections in.

Answer 5

It is recommended that you go to Google's guava toolkit... There are ready-made ones...

Answer 6

addAll() is enough