MultiMerge.java

package org.rdfhdt.hdt.iterator.utils;

import java.util.Comparator;
import java.util.Iterator;
import java.util.PriorityQueue;

public class MultiMerge<T> implements Iterator<T> {
	PriorityQueue<Source<T>> queue = new PriorityQueue<>();

	private static class Source<T> implements Comparable<Source<T>>{
		Comparator<T> comparator;
		Iterator<T> it;
		T entry;
		
		Source(Iterator<T> it, Comparator<T> comparator) {
			this.it = it;
			this.comparator = comparator;
		}
		
		public boolean read() {
			if(it.hasNext()) {
				entry = it.next();
				return true;
			} else {
				return false;
			}
		}

		@Override
		public int compareTo(Source<T> o) {
			return comparator.compare(this.entry, (T) o.entry);
		}
		
		
	}
	
	public MultiMerge(Iterator<Iterator<T>> it, Comparator<T> comparator){
		while(it.hasNext()) {
			Iterator<T> inner = it.next();
			
			if(inner.hasNext()) {
				Source<T> s = new Source<T>(inner, comparator);
				if(s.read()) {
					queue.add(s);
				}
			}
		}
	}
	
	@Override
	public boolean hasNext() {
		return !queue.isEmpty();
	}

	@Override
	public T next() {
		Source<T> item = queue.remove();
		
		T out = item.entry;
		
		if(item.read()) {
			queue.add(item);
		}
		
		return out;
	}

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

}