Source code

001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *   http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing,
013 * software distributed under the License is distributed on an
014 * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015 * KIND, either express or implied.  See the License for the
016 * specific language governing permissions and limitations
017 * under the License.
018 */
019package org.apache.reef.io.storage;
020
021import org.apache.reef.io.Tuple;
022import org.apache.reef.io.storage.util.TupleKeyComparator;
023
024import java.util.Comparator;
025import java.util.Iterator;
026import java.util.PriorityQueue;
027
028public class MergingIterator<T> implements Iterator<T> {
029  private final PriorityQueue<Tuple<T, Iterator<T>>> heap;
030
031  public MergingIterator(final Comparator<T> c, final Iterator<T>[] its) {
032    this.heap = new PriorityQueue<>(11, new TupleKeyComparator<T, Iterator<T>>(c));
033
034    for (final Iterator<T> it : its) {
035      final T b = it.hasNext() ? it.next() : null;
036      if (b != null) {
037        heap.add(new Tuple<>(b, it));
038      }
039    }
040  }
041
042  @Override
043  public boolean hasNext() {
044    return heap.size() != 0;
045  }
046
047  @Override
048  public T next() {
049    final Tuple<T, Iterator<T>> ret = heap.remove();
050    if (ret.getValue().hasNext()) {
051      heap.add(new Tuple<>(ret.getValue().next(), ret.getValue()));
052    }
053    return ret.getKey();
054  }
055
056  @Override
057  public void remove() {
058    throw new UnsupportedOperationException(
059        "Cannot remove entires from MergingIterator!");
060  }
061}