core-storage/src/main/java/org/apache/kylin/storage/gtrecord/PeekingImpl.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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 org.apache.kylin.storage.gtrecord;

import static org.apache.kylin.shaded.com.google.common.base.Preconditions.checkNotNull;
import static org.apache.kylin.shaded.com.google.common.base.Preconditions.checkState;

import java.util.Iterator;

import org.apache.kylin.shaded.com.google.common.collect.PeekingIterator;

/**
 * copied from guava, change iterator access modifier to public
 * 
 * Implementation of PeekingIterator that avoids peeking unless necessary.
 */
class PeekingImpl<E> implements PeekingIterator<E> {

    public final Iterator<? extends E> iterator;
    private boolean hasPeeked;
    private E peekedElement;

    public PeekingImpl(Iterator<? extends E> iterator) {
        this.iterator = checkNotNull(iterator);
    }

    @Override
    public boolean hasNext() {
        return hasPeeked || iterator.hasNext();
    }

    @Override
    public E next() {
        if (!hasPeeked) {
            return iterator.next();
        }
        E result = peekedElement;
        hasPeeked = false;
        peekedElement = null;
        return result;
    }

    @Override
    public void remove() {
        checkState(!hasPeeked, "Can't remove after you've peeked at next");
        iterator.remove();
    }

    @Override
    public E peek() {
        if (!hasPeeked) {
            peekedElement = iterator.next();
            hasPeeked = true;
        }
        return peekedElement;
    }
}