Iterator assignment issue Java

Question

So my assignment requires that I implement an interface in one of my class. The interface is a generic Iterator, which I will have to override the hasNext() and next() methods. I'm getting an error when I try to assign the instance ArrayList iterator to the instance Iterator.

Here's my interface:

public interface Iterator <E>
{
    boolean hasNext();
    E next();
    void remove();
}// end Iterator interface

And here's the class that implements that interface:

import java.util.*;
import java.io.*;

public class WordDatabase implements Iterator<String>
{
// Declaration
private List<String> aList;
private Iterator<String> aListIterator;

    /**** Other Class Methods Here *****/

@SuppressWarnings("unchecked")
public void shuffle()
{
    // Declaration
    int rand;
    String temp;

    // Statement
    // shuffling ArrayList
    for(int i = 0; i < getAlist(); i++)
    {
        rand = (int)(Math.random() * getAlist() - 1);

        // swapping two ArrayList entry

        temp = aList.get(i);
        aList.remove(i);
        aList.add(i, aList.get(rand));
        aList.remove(rand);
        aList.add(rand, temp);
    }

    aListIterator = aList.iterator();

    return;
}// end shuffle method

Eclipse is telling me that I need to cast aList.iterator() to Iterator<String> , but doing so throws an error java.util.AbstractList$Itr cannot be cast to Iterator . Can someone help me figure this problem out?

Answer 1

You can not do that as both Iterator objects belong to different packages.

You have to define your own List interface as you did for Iterator ; Define a method iterator() which returns object of your interface Iterator .

Answer 2

What i understood from the exception is You have defined your own Interface as Iterator so now there would not be any relation with List. So you can't Cast.

Answer 3

The java.util.List.iterator method returns an instance of java.util.Iterator , and not your my.special.Iterator interface. But you have declared the variable as my.special.Iterator interface. Though they have the same simple name, they are actually different types, and Eclipse wants you to cast it, which you can't because they are not related.

You would have to implement your own special List class as well, or avoid using the iterator method.

Answer 4

the Iterator<String> aListIterator is your iterator interface and the iterator returned by aList.iterator(); is java.util.Iterator.

The names are same but packages different (i am presuming that). So you cant cast them. But to actually iterate a list using your iterator you need to extend the list and implement your iterator inside it. which is what your WordDatabase class is trying to do. try to use an array in your class instead of a list.