com.microsoft.reef.io.storage.MergingIterator Maven / Gradle / Ivy

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/**
 * Copyright (C) 2013 Microsoft Corporation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *         http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.microsoft.reef.io.storage;

import com.microsoft.reef.io.Tuple;
import com.microsoft.reef.io.storage.util.TupleKeyComparator;

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

public class MergingIterator implements Iterator {
  private final PriorityQueue>> heap;

  public MergingIterator(final Comparator c, Iterator[] its) {
    this.heap = new PriorityQueue>>(11,
        new TupleKeyComparator>(c));

    for (Iterator it : its) {
      T b = it.hasNext() ? it.next() : null;
      if (b != null) {
        heap.add(new Tuple<>(b, it));
      }
    }
  }

  @Override
  public boolean hasNext() {
    return heap.size() != 0;
  }

  @Override
  public T next() {
    Tuple> ret = heap.remove();
    if (ret.getValue().hasNext()) {
      heap.add(new Tuple<>(ret.getValue().next(), ret.getValue()));
    }
    return ret.getKey();
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException(
        "Cannot remove entires from MergingIterator!");
  }
}