CODEWITHSUNDEEP
javagenerics
user2298337
user2298337

Reputation:

Missing type arguments for generic class

Using a library with an abstract class A and interfaces I and J, I get the following warning message when I extend / implement the class / interfaces:

Missing type arguments for generic class J<T>.

As a MWE, the classes are as follows (T and S are generic type parameters):

public abstract class A {}

public interface I<T extends A> {
    public <S extends T> void doStuff(J<? super S> param);
}

public interface J<T extends A> {
    public void doOtherStuff();
}

Here are my classes:

public class AExtended extends A {}

public class IImplemented implements I<AExtended> {
    @Override
    public void doStuff(J param) {}
}

Explicitly using the class AExtended as below does not properly implement doStuff() from I:

public class IImplemented implements I<AExtended> {
    @Override
    public void doStuff(J<AExtended> param) {}
}

Upvotes: 3

Views: 7883

Answers (2)

TNT
TNT

Reputation: 2920

You're not overriding doStuff in IImplemented because the method is not generic and the type bounds are not present. This version of doStuff should work for you:

public <S extends AExtended> void doStuff(J<? super S> param) {}

Notice that since the type of I is AExtended it is used appropriately here, and the lower bound in the wildcard type for J is also included.

Upvotes: 1

Tob&#237;as
Tob&#237;as

Reputation: 6297

try with:

public class IImplemented implements I<AExtended> {
   @Override
   public <S extends AExtended> void doStuff(J<? super S> param) {
      // ...
   }
}

Upvotes: 1

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