Iterates through (generic) List of List <<a1,a2>, <b1,b2,b3,b4>, <c1,c2,c3,c4,c5,c6,c7>> Generates output a1, b1, c1, a2, b2, c2, b3, c3, b4, c4,c5,c6,c7

GenericMultiListIterator.java

package com.expedia.sample;

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

public class MultiListIterator<E> implements Iterator<E> {

	private ArrayList<ArrayList<E>> useThisList;
	private int numOfList;
	private int[] sizeOfEachList;
	private int[] prevReturnedOfEachList;
	private int lastRetList;
	private int lastRetIndex;
			
	public MultiListIterator(ArrayList<ArrayList<E>> myList) {
		this.useThisList = myList;
		numOfList = myList.size();
		
		sizeOfEachList = new int[numOfList];
		prevReturnedOfEachList = new int[numOfList];
		for (int i = 0; i < numOfList; i++) {
			sizeOfEachList[i] = myList.get(i).size();
			prevReturnedOfEachList[i] = -1;
		}
		lastRetList = -1;
		lastRetIndex = -1;
		
		
	}
	public boolean hasNext() {
		int currentListIndex = lastRetList;
		int currentIndex = -1;
		int count = -1;
		
		do {
			currentListIndex = (currentListIndex + 1) % numOfList;
			currentIndex = prevReturnedOfEachList[currentListIndex] + 1;
			count++;
		}while(currentIndex == sizeOfEachList[currentListIndex] && count < numOfList);
		if (count == numOfList) {
			//System.out.println("False: Checked for currentList = " + currentListIndex + " and currentIndex = " + currentIndex);
			return false;
		}
		if ( currentIndex < sizeOfEachList[currentListIndex]) {
			//System.out.println("True : Checked for currentList = " + currentListIndex + " and currentIndex = " + currentIndex);
			return true;
		}
		return false;
	}

	public E next() {
		int currentListIndex = lastRetList;
		int currentIndex = -1;
		int count = -1;
		
		do {
			currentListIndex = (currentListIndex + 1) % numOfList;
			currentIndex = prevReturnedOfEachList[currentListIndex] + 1;
			count++;
		} while(currentIndex == sizeOfEachList[currentListIndex] && count < numOfList);
		if (count == numOfList) {
			//System.out.println("Cann't Return: Checked for currentList = " + currentListIndex + " and currentIndex = " + currentIndex);
			return null;
		}
		if ( currentIndex < sizeOfEachList[currentListIndex]) {
			//System.out.println("Returning : Checked for currentList = " + currentListIndex + " and currentIndex = " + currentIndex);
			lastRetList = currentListIndex;
			lastRetIndex = currentIndex;
			E temp = this.useThisList.get(lastRetList).get(lastRetIndex);
			prevReturnedOfEachList[lastRetList] = lastRetIndex;
			return temp;
			
		}
		return null;
	}
	
	public static void main(String[] args) {
		ArrayList<String> list1 = new ArrayList<String>();
		list1.add("a1");
		list1.add("a2");
		
		ArrayList<String> list2 = new ArrayList<String>();
		list2.add("b1");
		list2.add("b2");
		list2.add("b3");
		list2.add("b4");
		
		ArrayList<String> list3 = new ArrayList<String>();
		list3.add("c1");
		list3.add("c2");
		list3.add("c3");
		list3.add("c4");
		list3.add("c5");
		list3.add("c6");
		
		ArrayList<ArrayList<String>> finalList = new ArrayList<ArrayList<String>>();
		finalList.add(list1);
		finalList.add(list2);
		finalList.add(list3);
		
		
		MultiListIterator itr = new MultiListIterator<String>(finalList);
		itr.hasNext();
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		System.out.println(itr.next());
		
		
		ArrayList<Integer> list21 = new ArrayList<Integer>();
		list21.add(1);
		list21.add(2);
		
		ArrayList<Integer> list22 = new ArrayList<Integer>();
		
		list22.add(3);
		list22.add(4);
		list22.add(5);
		list22.add(6);
		
		ArrayList<Integer> list23 = new ArrayList<Integer>();
		list23.add(7);
		list23.add(8);
		list23.add(9);
		list23.add(10);
		list23.add(11);
		list23.add(12);
		
		ArrayList<ArrayList<Integer>> finalList1 = new ArrayList<ArrayList<Integer>>();
		finalList1.add(list21);
		finalList1.add(list22);
		finalList1.add(list23);
		
		System.out.println("Intger list");
		
		MultiListIterator itr1 = new MultiListIterator<Integer>(finalList1);
		itr1.hasNext();
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());
		System.out.println(itr1.next());

	}

	

}