Thread: creating an iterator without creating a class for it

I was asked to add an iterator to a class called MyLinkedList<E> which extends MyAbstractList<E> (abstract class) which implements MyList<E> (interface) .

Now I am asked to create the iterator without using the word "class"....I know how to create an iterator using a private class but wihtout using the word class at all? I am out of ideas....

MyLinkedList has an inner class which is:
private static class Node<E>

I tried implementing the Iterator interface for MyLinkedList...

But then how do I return the Itarator ? how do I instanciate it?
REturning new iterator does not help since then it doesn;t have the size of the list.
Usually when I have its own class I have no problem returning new itereator since it keeps in its class the size of the outter class' list, but when I do it like this , it creates a new list so size is 0....I thought of adding the implementation to the node but then it makes no sense since the node should;t know it is a part of a list....

Any ideas?
Inner class is not forbidden...only using the class word is...if it makes any sense

First thank you very much for the help.

I tried doing it but my Iterator wouldn;t iterate...it prints the first 1 only...
It should (by what we were asked) start from the end to teh start so I set it;s start point to the size of the list and each time (since index starts from 0) I firstly decrease it then returns the right element by the index....well this is the idea.


In order to see what happens I tried creating another method to return the current index but for some reason my main doesn;t recognize this method and I dun get why...this is what I have:

 Iterator<E> it=new Iterator<E>()
	{
		int index=size;	
 
		@Override
		public E next()
		{		
 
			index--;
			return (E)get(index);							
 
		}
		@Override
		public void remove() {
			// TODO Auto-generated method stub
 
		}
		@Override
		public boolean hasNext() {
			// TODO Auto-generated method stub
			return false;
		}
		public int getIndex()
		{return index;}
 
	};
 
 
	public Iterator<E> iterator()
	{
		return  it;
	}

This is in my MyLinkedList class.

On main I have

Iterator it=lst.iterator();
 
		it.getIndex();

second line is treated as error....anything I did wrong?

--- Update ---

I added printing inside the next() method and for some reason even though the list's size is not 0 when I write in the iterator class I created

int index=size

it saves index as 0.
I am confused.
It recognizes the name of the variable but does not get the value....

size is declared on the MyList interface while I wrote my Iterator for MyLinkedList

Please read this topic to learn how to post code correctly and then apply it.

Thanks.

forgot to add this:

@Override
		public boolean hasNext() {
		if(index>0)
			return true;
			return false;
		}

Does not matter much though.

The only problem is the initial value it gets for index ...
It works when I enter a number but not when I set size.
I guess it happens when it precompiles and not when I ask to get an Iterator so I should have a method to reset the Iterator but it doesn;t seem like I can add methods....and I can;t get to the inner classes parameter from teh outter class so it must be inside the inner class so I am confused.

--- Update ---

Ok I changed it to

public  Iterator<E> iterator()
	{
		return new Iterator<E>(){
			int index=size;
 
			@Override
			public E next()
			{					
				index--;
				return (E)get(index);							
 
			}
			@Override
			public void remove() {
				// TODO Auto-generated method stub
 
			}
			@Override
			public boolean hasNext() {
				if(index>0)
					return true;
				return false;
			}
		};	
	}

And now it seems to work....I don;t get it still though >.<
What was wrong with the previous version and what bugs me more is it did not have a return statement but it didn;t seem to care.....

Originally Posted by andbin

1) [important] Your list is a "linked" list ..... but get(index) has to scan the linked list to find the item at that index! Remember that the iterator can (and should) have an "intimate" vision on the internal structure of the linked list. Thus the iterator should carry the iteration in the smart way .... not in the trivial way call-the-get-on-each-next.

I agree. Unfortunately we were asked to use existing methods.
I would write a method that scans till current index -1 or something, pretty much does the same but without using external method.
On the other hand we are asked to write it wisely so I guess I will still do it.

Originally Posted by andbin

2) If you have used the "generics" in an appropriate and consistent way, the cast (E)get(index) is not necessary.

Seems Java asked to add casting, but I will look into it again, may be a leftover from my previous pathetic attempts.

Originally Posted by andbin

3) If you don't want to implement remove() with the appropriate behaviour, you can leave it empty but generally it's more common and useful to throw a java.lang.UnsupportedOperationException just to signal that it's not supported.

3. Thank you, I will add it.


Thank you very much for the help