Java tutorial
/* * Copyright 2011,2012 Metamarkets Group Inc. * * 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 sg.atom.utils._beta.functional; import com.google.common.collect.Iterators; import com.google.common.collect.PeekingIterator; import java.util.Comparator; import java.util.Iterator; import java.util.List; import java.util.NoSuchElementException; import java.util.PriorityQueue; /** */ public class MergeIterator<T> implements Iterator<T> { private final PriorityQueue<PeekingIterator<T>> pQueue; public MergeIterator(final Comparator<T> comparator, List<Iterator<T>> iterators) { pQueue = new PriorityQueue<PeekingIterator<T>>(16, new Comparator<PeekingIterator<T>>() { @Override public int compare(PeekingIterator<T> lhs, PeekingIterator<T> rhs) { return comparator.compare(lhs.peek(), rhs.peek()); } }); for (Iterator<T> iterator : iterators) { final PeekingIterator<T> iter = Iterators.peekingIterator(iterator); if (iter != null && iter.hasNext()) { pQueue.add(iter); } } } @Override public boolean hasNext() { return !pQueue.isEmpty(); } @Override public T next() { if (!hasNext()) { throw new NoSuchElementException(); } PeekingIterator<T> retIt = pQueue.remove(); T retVal = retIt.next(); if (retIt.hasNext()) { pQueue.add(retIt); } return retVal; } @Override public void remove() { throw new UnsupportedOperationException(); } }