Implement interface with two generics

Question

I've got a task as a part of my homework and I can not get over it.

The code of the transformer interface is the following:

public interface Transformer<FROM, TO> {
    TO transform(FROM value);
}

The code of the PersonSubscriberTransformer class looks like this so far:

public class PersonSubscriberTransformer<FROM, TO> implements Transformer {
    private Predicate<Person> predicate;
    public PersonSubscriberTransformer(Predicate<Person> predicate) {
        this.predicate = predicate;
    }
    @Override
    public Object transform(Object value) {
        return null;
    }
  }

The paramether of the transform method should be List<Person> and it should return a List<Subscriber>. As I'm changing the paramether I got an error saying I should pull the method to the Transformer interface.

What would be the solution to implement this method in the correct way?

Does this answer your question? Implementation of generic interface with specific type in Java — Chaosfire
– Chaosfire, Commented Jan 17, 2024 at 16:58

Unmitigated · Accepted Answer · 2024-01-17 16:49:20Z

6

Based on the intended signature of transform, FROM should be List<Person> and TO should be List<Subscriber>. The class itself should not be generic.

public class PersonSubscriberTransformer implements Transformer<List<Person>, List<Subscriber>> {
    // constructor...
    
    @Override
    public List<Subscriber> transform(List<Person> persons) {
        // complete this method...
        return null;
    }
}

answered Jan 17, 2024 at 16:49

Unmitigated

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