Iterator over Iterators

843793

Hi,

I am trying to write an ItIterator class which would iterate over the elements of multiple iterator.

import java.util.ArrayList;
import java.util.Iterator;


public class ItIterator<T> implements Iterator<T> {

	private Iterator<T> currIterator=null;
	private ArrayList<Iterator<T>> arr;
	private Iterator<Iterator<T>> arrIterator;
	
	public ItIterator()
	{
		arr=new ArrayList<Iterator<T>>();
		arrIterator=arr.iterator();
	}
	
	public void add(Iterator<T> e)
	{
		arr.add(e);
	}
	
	
	@Override
	public boolean hasNext() 
	{
		if(currIterator!=null && currIterator.hasNext())
			return true;
		
		while(arrIterator.hasNext())
		{
			currIterator=arrIterator.next();
			if(currIterator.hasNext())
				return true;
		}
		return false;
	}

	@Override
	public T next() 
	{
		if(currIterator!=null && currIterator.hasNext())
			return currIterator.next();
		
		while(arrIterator.hasNext())
		{
			currIterator=arrIterator.next();
			if(currIterator.hasNext())
				return currIterator.next();
		}
		return null;
	}

	@Override
	public void remove() 
	{
		if(currIterator!=null && currIterator.hasNext())
			currIterator.remove();
		
		while(arrIterator.hasNext())
		{
			currIterator=arrIterator.next();
			if(currIterator.hasNext())
			{
				currIterator.remove();
				return;
			}
		}
		
	}

}

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;


public class Test 
{
	
	
	
	public static void main(String args[])
	{
		ItIterator<Integer> i=new ItIterator<Integer>();
		
		ArrayList<Integer> a=new ArrayList<Integer>();
		a.add(1);
		a.add(2);
		a.add(3);
		ArrayList<Integer> b=new ArrayList<Integer>();
		b.add(4);
		b.add(5);
		b.add(6);
		
		i.add(a.iterator());
		i.add(b.iterator());
		
		while(i.hasNext())
			System.out.println(i.next().toString());
		
	}
	

}

Te above code complies without any error but gives a runtime exception as follows:

Exception in thread "main" java.util.ConcurrentModificationException
	at java.util.AbstractList$Itr.checkForComodification(Unknown Source)
	at java.util.AbstractList$Itr.next(Unknown Source)
	at ItIterator.hasNext(ItIterator.java:31)
	at Test.main(Test.java:28)

If someone could help me out solving this exception that would be great.

jtahlborn

you cannot initialize arrIterator until you are done calling add().

jtahlborn

also, to really make this class useful you should make all your internal types "<? extends T>".

843793

Thanks jtahlborn. I modified the add code as:

public void add(Iterator<T> e)
	{
		arr.add(e);
		arrIterator=arr.iterator();
	}