CODEWITHSUNDEEP
javagenerics
Gijs Peters
Gijs Peters

Reputation: 31

Return object typed with generic class type

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.

Upvotes: 3

Views: 87

Answers (1)

Pavneet_Singh
Pavneet_Singh

Reputation: 37404

by default T is replaced with Object so this is type inference based on the target so try this

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

Upvotes: 1

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