返回使用泛型类类型键入的对象

Question

The code below contains a getter to a Set of objects with class T:

public class Cube <T extends State> {

   private Set<T> states = new HashSet<>();

   public Set<T> getStates() {
      return states;
   }

} 

Which seemed to me the valid way to return a the Set of states. However, it returns a set of Objects instead. Trying to use:

Cube<DestinationState> cube = new Cube<>();
Set<DestinationState> set = cube.getStates();

Yields a compile error on the second line:

Error:(187, 61) java: incompatible types: java.lang.Object cannot be converted to nl.gijspeters.pubint.graph.state.DestinationState

State is a generic interface with multiple implementation classes (among which DestinationState) and subinterfaces.

This may very well be a duplicate question (as it seems quite basic), however, I was not able to find the answer.

Answer 1

默认情况下， T替换为Object因此这是基于目标的类型推断，所以试试这个

Set<DestinationState> set = cube<DestinationState>.getStates();