com.googlecode.cqengine.resultset.iterator.ConcatenatingIterator Maven / Gradle / Ivy

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Collection Query Engine: NoSQL indexing and query engine for Java collections with ultra-low latency

There is a newer version: 3.6.0

/**
 * Copyright 2012-2015 Niall Gallagher
 *
 * 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.googlecode.cqengine.resultset.iterator;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * @author Niall Gallagher
 */
public abstract class ConcatenatingIterator extends UnmodifiableIterator {

    private Iterator currentIterator = null;


    @Override
    public boolean hasNext() {
        while (currentIterator == null || !currentIterator.hasNext()) {
            currentIterator = getNextIterator();
            if (currentIterator == null) {
                return false;
            }
        }
        return true;
    }

    @Override
    public O next() {
        Iterator currentIterator = this.currentIterator;
        if (currentIterator == null) {
            throw new NoSuchElementException("No more elements");
        }
        return currentIterator.next();
    }

    public abstract Iterator getNextIterator();

    public static  ConcatenatingIterator concatenate(final Iterable> iterators) {
        return new ConcatenatingIterator() {
            final Iterator> iteratorIterator = iterators.iterator();
            @Override
            public Iterator getNextIterator() {
                return iteratorIterator.hasNext() ? iteratorIterator.next() : null;
            }
        };
    }
}