issue with java generics in an interface

Question

I am implementing an interface that can manage a stack, I have the following code:

public interface Stack <E>{
    public int size();
    public boolean isEmpty();
    public E top();
    public void push(E item);    //error here

and the class that implements this interface has:

public class StackArray<E> implements Stack{
    private E array[];
    private int top=-1;
    public StackArray(int n){
        array=(E[]) Array.newInstance(null, n); ////not quite sure about this
    }
    //more code
    public void push(E item){
        if (top==array.length-1) System.out.println("stack is full");
        else{
            top++;
            array[top]=item;
        }
    }

the error that I got is the I am not overriding the push method, I see that both have the same signature, but I am not quite sure.

how can I fix that?

When you write implements Stack you are in fact implementing Stack<Object>. — Guillaume Poussel
– Guillaume Poussel, Commented Oct 13, 2013 at 14:44
Be careful about reporting where errors are; it's usually best to just post the error message. The error is not in your interface, it's in your implementing class. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Oct 13, 2013 at 14:46
This is why you should always use the @Override annotation, your IDE would have inmidiatly informed you what the problem was — 0x6C38
– 0x6C38, Commented Oct 13, 2013 at 14:47

chrylis -cautiouslyoptimistic- · Accepted Answer · 2013-10-13 14:44:19Z

5

You're not binding the E parameter in StackArray to the E parameter in Stack. Use this declaration:

public class StackArray<E> implements Stack<E>

answered Oct 13, 2013 at 14:44

chrylis -cautiouslyoptimistic-

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