Custom iterator using generic types

Question

I'm trying to build a extension of ArrayList and build a custom Iterator for it, all in generic types, and I'm getting errors before compilation which I do not understand.

public class GenerateurBiGramme <T> extends ArrayList <T> {
    public Iterator<Pair<T,T>> iterator(int delta){
        return new BiGramme<>(delta);
    }
    public class BiGramme <T> implements Iterator<Pair<T, T>>{
        int premier = 0;
        int dernier = 1;
        int delta;
        public Pair<T, T> next() {
            Pair<T,T> temp = new Pair<T,T>(get(this.debut),get(this.dernier));
            return temp;
        }

My IDE is telling me that "Pair(T,T) in Pair cannot be applied to (T,T).

I don't understand what it means by that.

Thank you for your help!

EDIT: here is my "Pair" class:

public class Pair<T, U> {
    public T premiere;
    public U deuxieme;

    public Pair( T premiere, U deuxieme ) {
        this.premiere = premiere;
        this.deuxieme = deuxieme;
    }
}

Basically, I'm going to feed a table into the generator, and I intend to use "premier" and "dernier" to create pairs at a set distance from one another...

Is that org.apache.commons.lang3.tuple.Pair or some other Pair class? If it's your own class, can you show us the code please? — Dawood ibn Kareem
– Dawood ibn Kareem, Commented Jun 9, 2018 at 2:21
Could you post your whole class? There's so much to guess about BiGramme, this.debut, this.dernier... — Mạnh Quyết Nguyễn
– Mạnh Quyết Nguyễn, Commented Jun 9, 2018 at 2:28

Dawood ibn Kareem · Accepted Answer · 2018-06-09 03:36:36Z

2

Your problem is that in your declaration public class BiGramme <T>, the T hides the T that you declared in public class GenerateurBiGramme <T>. You now have two different type parameters to GenerateurBiGramme.BiGramme, but unfortunately, they're both called T.

You don't need the T in the declaration of BiGramme, because it's an inner class, so it already has access to the type parameters of the outer class, GenerateurBiGramme. Just change the declaration to public class BiGramme, without the T. Also remove the <> from the line return new BiGramme(delta);. This worked for me.

answered Jun 9, 2018 at 3:36

Dawood ibn Kareem

80.2k15 gold badges102 silver badges112 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Custom iterator using generic types

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related