SortedReduceIterator.java

package org.rdfhdt.hdt.iterator.utils;

import java.util.Iterator;
import java.util.NoSuchElementException;

public class SortedReduceIterator<T> implements Iterator<T> {
	
	Iterator<T> it;
	Reducer<T> reducer;
	T nextValue;
	
	public SortedReduceIterator(Iterator<T> it, Reducer<T> reducer) {
		this.it=it;
		this.reducer=reducer;
		
		if(it.hasNext()) {
			nextValue = it.next();
		}
	}

	@Override
	public boolean hasNext() {
		return nextValue!=null;
	}

	@Override
	public T next() {
		if(nextValue==null) {
			throw new NoSuchElementException();
		}
		
		T returned = nextValue;
		
		while(true) {
			if(it.hasNext()) {
				nextValue = it.next();

				T reduced = reducer.reduce(returned, nextValue);
				if(reduced!=null) {
					returned=reduced;
				} else {
					break;
				}
			} else {
				nextValue=null;
				break;
			}
		}
		
		return returned;
	}

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