@Override
    public Integer next() {
        if (!hasNext()) {
            throw new IllegalArgumentException();
        }
        Integer val = nextVal;
        nextVal = null;
        return val;
    }
Date 04/17/2017
@author Tushar Roy

Given a nested list of integers, implement an iterator to flatten it.
Each element is either an integer, or a list -- whose elements may also be integers or other lists.
Example 1:
Given the list [[1,1],2,[1,1]],
By calling next repeatedly until hasNext returns false, the order of elements returned by next should be: [1,1,2,1,1].

https://leetcode.com/problems/flatten-nested-list-iterator/
src/com/interview/misc/NestedIterator.java