Get rid of Unchecked overriding: return type requires unchecked conversion

Example code similar to my code.

public interface Builder<B, A> {
B build(A a);
}

public class ClientBuilder implements Builder<String, Integer> {
@Override
public String build(Integer i) {
return i.toString();
}
}

public abstract class Client<B> {
protected abstract <A> Builder<B, A> getBuilder();
}

public class ClientClient extends Client<String> {

@Override
protected Builder<String, Integer> getBuilder() {
return null;
}
}


In my ClientClient class I get a warning that says the following:

ClientClient

Unchecked overriding: return type requires unchecked conversion.Found 'Builder<java.lang.String,java.lang.Integer>', required 'Builder<java.lang.String,A>

Unchecked overriding: return type requires unchecked conversion.Found 'Builder<java.lang.String,java.lang.Integer>', required 'Builder<java.lang.String,A>

Is there something I can do to get rid of this error?
I could use @SuppressWarnings("unchecked"), but that doesn't feel right.

@SuppressWarnings("unchecked")

In my example A is always an Integer but in my real code A can be one of two objects.

A

Integer

A

I guess I could also have two methods in my interface like this:

public interface Builder<B> {
B build(Integer i);
B build(String s);
}


Function<A,B>

<A>

Builder<B, A>

1 Answer
1

This isn't overriding the method correctly:

protected Builder<String, Integer> getBuilder() {
return null;
}


You're missing the type variable.

Either declare it correctly:

protected <A> Builder<String, A> getBuilder() {
return null;
}


or change the class declaration to allow you to provide the second type parameter:

public abstract class Client<B, A> {
protected abstract Builder<B, A> getBuilder();
}


Object

getBuilder()

Integer

@SuppressWarnings

null

Builder

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