io.druid.java.util.common.guava.MergeIterator Maven / Gradle / Ivy
/*
* Licensed to Metamarkets Group Inc. (Metamarkets) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. Metamarkets licenses this file
* to you 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 io.druid.java.util.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 implements Iterator
{
private final PriorityQueue> pQueue;
public MergeIterator(
final Comparator comparator,
List> iterators
)
{
pQueue = new PriorityQueue<>(
16,
new Comparator>()
{
@Override
public int compare(PeekingIterator lhs, PeekingIterator rhs)
{
return comparator.compare(lhs.peek(), rhs.peek());
}
}
);
for (Iterator iterator : iterators) {
final PeekingIterator 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 retIt = pQueue.remove();
T retVal = retIt.next();
if (retIt.hasNext()) {
pQueue.add(retIt);
}
return retVal;
}
@Override
public void remove()
{
throw new UnsupportedOperationException();
}
}