对于Set类型，未定义（）方法

Question

when i'm trying to run this code:

Set<Set<Integer>> s1 = Set.of(Set.of(), Set.of(1));

i'm getting this error:

The method of() is undefined for the type Set
The method of(int) is undefined for the type Set

I'm using Java 8. What is wrong? :/

Answer 1

These methods were introduced in Java SE 9. See the @since in the source code on the API docs. You'll need to upgrade to a current version of Java or use something else, such as new HashSet<>(Arrays.asList(fred, jim, sheila)) .