com.metamx.common.guava.MergeIterator.java Source code

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Here is the source code for com.metamx.common.guava.MergeIterator.java

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/*
 * 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 com.metamx.common.guava;

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<>(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();
    }
}