Generics: Implementing a set class

[Gil Shoam]

Hi,

I'm trying to implement a generic class used to define a set of different types. I'm trying to add a constructor that stores an array into the set. for some reason the add method does not work. (The compiler says: "Add (E) in arrayList can not be applied to (E)"

Here is my code:

public class Set<E> {

    private ArrayList<E> elements;


    public Set() {
        elements = new ArrayList<E>();

    }

    public <E> void setFromArray(E[] inputArray) {
        elements = new ArrayList<E>(inputArray.length);

        for (E e : inputArray)
            elements.add(e);

    }
}

Any idea why It won't add the elements?

Thanks

[Stephan van Hulst]

Because you are redeclaring the type parameter E in your method.

Why are you using such a method anyway? Why not provide a constructor that takes an array?

[Gil Shoam]

Stephan van Hulst wrote:

Why are you using such a method anyway? Why not provide a constructor that takes an array?

You are right.. that is what I meant to do.....

(it's 2:30 a.m here... )

but anyway can you elaborate on this:

Stephan van Hulst wrote:Because you are redeclaring the type parameter E in your method.

[Paul Clapham]

First you declare a type variable called <E> in line 1. Then you declare another type variable in line 11. It's also called <E>, which leads to all kinds of confusion, especially since it isn't the same as the one in line 1.

Presumably you wanted to use the <E> declared at the class level. In which case don't declare another <E> at the method level.