alexey-pelykh commented on code in PR #509: URL: https://github.com/apache/commons-collections/pull/509#discussion_r1697875375
########## src/main/java/org/apache/commons/collections4/iterators/CartesianProductIterator.java: ########## @@ -0,0 +1,157 @@ +/* + * 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.commons.collections4.iterators; + +import java.util.ArrayList; +import java.util.Arrays; +import java.util.Iterator; +import java.util.List; +import java.util.NoSuchElementException; +import java.util.Objects; + +/** + * This iterator creates a Cartesian product of the input iterables, + * equivalent to nested for-loops. + * <p> + * The iterables provided to the constructor are used in reverse order, each + * until exhaustion before proceeding to the next element of the prior iterable + * and repeating. Consider the following example: + * + * <pre>{@code + * List<Character> iterable1 = Arrays.asList('A', 'B', 'C'); + * List<Character> iterable2 = Arrays.asList('1', '2', '3'); + * CartesianProductIterator<Character> it = new CartesianProductIterator<>( + * iterable1, + * iterable2); + * while (it.hasNext()) { + * List<Character> tuple = it.next(); + * System.out.println(tuple.get(0) + ", " + tuple.get(1)); + * } + * }</pre> + * + * The output will be: + * + * <pre> + * A, 1 + * A, 2 + * A, 3 + * B, 1 + * B, 2 + * B, 3 + * C, 1 + * C, 2 + * C, 3 + * </pre> + * <p> + * The {@code remove()} operation is not supported, and will throw an + * {@code UnsupportedOperationException}. + * + * @param <E> the type of the objects being permuted + * @since 4.5.0 + */ +public class CartesianProductIterator<E> implements Iterator<List<E>> { + + /** + * The iterables to create the Cartesian product from. + */ + private final List<Iterable<? extends E>> iterables; + + /** + * The iterators to generate the Cartesian product tuple from. + */ + private final List<Iterator<? extends E>> iterators; + + /** + * The previous generated tuple of elements. + */ + private List<E> previousTuple; + + /** + * Standard constructor for this class. + * + * @param iterables the iterables to create the Cartesian product from + * @throws NullPointerException if any of the iterables is null + */ + public CartesianProductIterator(final Iterable<? extends E>... iterables) { + Objects.requireNonNull(iterables, "iterables"); + this.iterables = Arrays.asList(iterables); + this.iterators = new ArrayList<>(iterables.length); + for (final Iterable<? extends E> iterable : iterables) { + Objects.requireNonNull(iterable, "iterable"); + final Iterator<? extends E> iterator = iterable.iterator(); + if (iterator.hasNext()) { + iterators.add(iterator); + } else { + iterators.clear(); + break; + } + } + } + + /** + * Indicates if there are more tuples to return. + * + * @return true if there are more tuples, otherwise false + */ + @Override + public boolean hasNext() { + for (final Iterator<? extends E> iterator : iterators) { Review Comment: While I agree that it's less verbose, I don't think that justifies all the call chain and objects creation that need to happen in that line. Is this change request a blocking one? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
