ItemIterator.java

package com.asana.iterator;

import java.util.Iterator;

/**
 * "Flattens" a page iterator, returning a single item at a time, loading pages from the page iterator on demand.
 */
public class ItemIterator<T> implements Iterator<T> {
    PageIterator<T> pages;
    Iterator<T> current;

    public ItemIterator(PageIterator<T> pages) {
        this.pages = pages;
        this.current = null;
    }

    @Override
    public boolean hasNext() {
        return (current != null && current.hasNext()) || pages.hasNext();
    }

    @Override
    public T next() {
        if (current == null || !current.hasNext()) {
            current = pages.next().iterator();
        }
        return current.next();
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException();
    }
}