Question

So I am attempting to create a LinkedHashedDictionary’s Iterator member for a homework assignment, however I am having multiple issues regarding its types.

Iterator Interface:

package nhUtilities.containers2;

public interface Iterator<Element> extends Cloneable, java.util.Iterator<Element>
{
  public void reset ();
  public void advance ();
  public boolean done ();
  public Element get ();
  public boolean equals (Object obj);
  public boolean traverses (Object container);
  public Object clone ();
  public void setEqualTo (Iterator<Element> other);
  public boolean hasNext ();
  public Element next ();
  public void remove ();
}

In my code, I have a private class called EntryIterator. It extends an AbstractIterator, but implements the Iterator above.

My current implementation is as follows:

private class EntryIterator<Element> extends AbstractIterator<Element>
    implements Iterator<Element>
    {

        protected Iterator<Key> keyIterator;
        protected Dictionary<Key,Value> dictionary;

        public EntryIterator(Dictionary<Key,Value> dictionary)
        {
            keyIterator = keys.iterator();
            this.dictionary = dictionary;
        }

        public void reset()
        { keyIterator = keys.iterator(); }

        /**
         * @Requrie !this.done()
         */
        public void advance()
        { keyIterator.advance(); }

        public boolean done()
        { return keyIterator.done(); }

        // public Entry<Key,Value> get()
        // Violates initial Interface: Results in compile error.
        // Return type must be "Element"
        public Element get()
        {
            Key key = keyIterator.get();
            Value value = dictionary.get(keyIterator.get());
            return (Element) new Entry<Key,Value>(key, value);
        }

        public boolean traverses(Object container)
        {
            // TODO Iterator traverses
            return false;
        }

        public void setEqualTo(Iterator<Element> other)
        {
            this.keyIterator = ((EntryIterator<Element>) other).keyIterator;
            this.dictionary = ((EntryIterator<Element>) other).dictionary;
        }

    }

I have done multiple varieties of this class regarding its types, but none of them seem to be compatible with my Dictionary. Should I keep the formatting as is above, I get an error on my Dictionary’s iterator() function:

public Iterator<Entry<Key,Value>> iterator()
{
    return new EntryIterator<Entry<Key,Value>>(this);
}

The error states it is “The return type is incompatible for Dictionary.iterator()”

Should I change the type of the EntryIterator class’ type to:

private class EntryIterator<eEntry<Key,Value>> extends AbstractIterator<Element>
implements Iterator<Element>

I simply get an error saying “Syntax error expected on token ‘<‘” as well as another incompatibility error on my Dictionary.Iterator() function.

Can someone point me in the right direction as to how I can link up all of these different types to get them to return what my contract for Dictionary demands?

I have attempted asking my question during the class, via email to the instructor, as well as one on one merely to be avoided. Any help would be much appreciated.

Answer 1

So, the problem was actually with my class instantiation… Here for everyone with similar issues:

 private class EntryIterator extends AbstractIterator<Entry<Key,Value>> implements 
nhUtilities.containers2.Iterator<Entry<Key, Value>>