/*
 * 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
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package org.apache.commons.collections4.iterators;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

import org.apache.commons.collections4.FluentIterable;

Provides an interleaved iteration over the elements contained in a collection of Iterators.

Given two Iterator instances A and B, the next method on this iterator will switch between A.next() and B.next() until both iterators are exhausted.

Since:4.1
/** * Provides an interleaved iteration over the elements contained in a * collection of Iterators. * <p> * Given two {@link Iterator} instances {@code A} and {@code B}, the * {@link #next} method on this iterator will switch between {@code A.next()} * and {@code B.next()} until both iterators are exhausted. * * @since 4.1 */
public class ZippingIterator<E> implements Iterator<E> {
The Iterators to evaluate.
/** The {@link Iterator}s to evaluate. */
private final Iterator<Iterator<? extends E>> iterators;
The next iterator to use for next().
/** The next iterator to use for next(). */
private Iterator<? extends E> nextIterator = null;
The last iterator which was used for next().
/** The last iterator which was used for next(). */
private Iterator<? extends E> lastReturned = null; // Constructors // ----------------------------------------------------------------------
Constructs a new ZippingIterator that will provide interleaved iteration over the two given iterators.
Params:
  • a – the first child iterator
  • b – the second child iterator
Throws:
/** * Constructs a new <code>ZippingIterator</code> that will provide * interleaved iteration over the two given iterators. * * @param a the first child iterator * @param b the second child iterator * @throws NullPointerException if either iterator is null */
@SuppressWarnings("unchecked") public ZippingIterator(final Iterator<? extends E> a, final Iterator<? extends E> b) { this(new Iterator[] {a, b}); }
Constructs a new ZippingIterator that will provide interleaved iteration over the three given iterators.
Params:
  • a – the first child iterator
  • b – the second child iterator
  • c – the third child iterator
Throws:
/** * Constructs a new <code>ZippingIterator</code> that will provide * interleaved iteration over the three given iterators. * * @param a the first child iterator * @param b the second child iterator * @param c the third child iterator * @throws NullPointerException if either iterator is null */
@SuppressWarnings("unchecked") public ZippingIterator(final Iterator<? extends E> a, final Iterator<? extends E> b, final Iterator<? extends E> c) { this(new Iterator[] {a, b, c}); }
Constructs a new ZippingIterator that will provide interleaved iteration of the specified iterators.
Params:
  • iterators – the array of iterators
Throws:
/** * Constructs a new <code>ZippingIterator</code> that will provide * interleaved iteration of the specified iterators. * * @param iterators the array of iterators * @throws NullPointerException if any iterator is null */
public ZippingIterator(final Iterator<? extends E>... iterators) { // create a mutable list to be able to remove exhausted iterators final List<Iterator<? extends E>> list = new ArrayList<>(); for (final Iterator<? extends E> iterator : iterators) { if (iterator == null) { throw new NullPointerException("Iterator must not be null."); } list.add(iterator); } this.iterators = FluentIterable.of(list).loop().iterator(); } // Iterator Methods // -------------------------------------------------------------------
Returns true if any child iterator has remaining elements.
Returns:true if this iterator has remaining elements
/** * Returns {@code true} if any child iterator has remaining elements. * * @return true if this iterator has remaining elements */
@Override public boolean hasNext() { // the next iterator has already been determined // this might happen if hasNext() is called multiple if (nextIterator != null) { return true; } while(iterators.hasNext()) { final Iterator<? extends E> childIterator = iterators.next(); if (childIterator.hasNext()) { nextIterator = childIterator; return true; } // iterator is exhausted, remove it iterators.remove(); } return false; }
Returns the next element from a child iterator.
Throws:
Returns:the next interleaved element
/** * Returns the next element from a child iterator. * * @return the next interleaved element * @throws NoSuchElementException if no child iterator has any more elements */
@Override public E next() throws NoSuchElementException { if (!hasNext()) { throw new NoSuchElementException(); } final E val = nextIterator.next(); lastReturned = nextIterator; nextIterator = null; return val; }
Removes the last returned element from the child iterator that produced it.
Throws:
  • IllegalStateException – if there is no last returned element, or if the last returned element has already been removed
/** * Removes the last returned element from the child iterator that produced it. * * @throws IllegalStateException if there is no last returned element, or if * the last returned element has already been removed */
@Override public void remove() { if (lastReturned == null) { throw new IllegalStateException("No value can be removed at present"); } lastReturned.remove(); lastReturned = null; } }