CODEWITHSUNDEEP
javagenericshashmapoverriding
Merni
Merni

Reputation: 2912

addAll(Collection).. is not applicable for the arguments (Iterable)

I have created a HashSet class that extends HashSet in Java. If I just add one element the code is fine. But when I use addAll it states the following:

The method addAll(Collection<? extends Number>) in the type MyHashSet<Number> is not applicable for the arguments (Iterable<Integer>)

What is the reason and how can I come around it?

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;

public class MyHashSet<E> extends HashSet<E> {
private int count;
public int Count() { 
    return count;
}

@Override public boolean add(E e) {
    count++;
    return super.add(e);    
}

@Override public boolean addAll(Collection<? extends E> c) {
    count += c.size();
    return super.addAll(c);
}

public static void main(String[] args) {
    MyHashSet<Number> hs = new MyHashSet<>();
    hs.add(new Integer(1));
    Iterable<Integer> integers = new ArrayList<Integer>(Arrays.asList(1,3,5,7,9));
    hs.addAll(integers);
}
}

Upvotes: 0

Views: 5001

Answers (1)

Marko Topolnik
Marko Topolnik

Reputation: 200168

Declare integers as

Collection<Integer> integers;

because addAll does not support arbitrary Iterables. This is due to historical reasons, Iterable is a retrofitted interface and the method signature could not be changed without breakage.

Upvotes: 5

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