Source code

001///////////////////////////////////////////////////////////////////////////////////////////////
002// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
003// Copyright (C) 2001-2025 the original author or authors.
004//
005// This library is free software; you can redistribute it and/or
006// modify it under the terms of the GNU Lesser General Public
007// License as published by the Free Software Foundation; either
008// version 2.1 of the License, or (at your option) any later version.
009//
010// This library is distributed in the hope that it will be useful,
011// but WITHOUT ANY WARRANTY; without even the implied warranty of
012// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
013// Lesser General Public License for more details.
014//
015// You should have received a copy of the GNU Lesser General Public
016// License along with this library; if not, write to the Free Software
017// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
018///////////////////////////////////////////////////////////////////////////////////////////////
019
020package com.puppycrawl.tools.checkstyle.utils;
021
022import java.util.Arrays;
023import java.util.Collection;
024import java.util.Collections;
025import java.util.List;
026import java.util.Map;
027import java.util.Set;
028
029/**
030 * <div>Note: it simply wraps the existing JDK methods to provide a workaround
031 * for Pitest survival on mutation for removal of immutable wrapping,
032 * see #13127 for more details.
033 * </div>
034 *
035 */
036public final class UnmodifiableCollectionUtil {
037
038 /**
039 * Private constructor for UnmodifiableCollectionUtil.
040 *
041 */
042 private UnmodifiableCollectionUtil() {
043 }
044
045 /**
046 * Creates an unmodifiable list based on the provided collection.
047 *
048 * @param collection the collection to create an unmodifiable list from
049 * @param <T> the type of elements in the set
050 * @return an unmodifiable list containing the elements from the provided collection
051 */
052 public static <T> List<T> unmodifiableList(List<T> collection) {
053 return Collections.unmodifiableList(collection);
054 }
055
056 /**
057 * Returns an unmodifiable view of a List containing elements of a specific type.
058 *
059 * @param items The List of items to make unmodifiable.
060 * @param elementType The Class object representing the type of elements in the list.
061 * @param <S> The generic type of elements in the input Collection.
062 * @param <T> The type of elements in the resulting unmodifiable List.
063 * @return An unmodifiable List containing elements of the specified type.
064 */
065 public static <S, T> List<T> unmodifiableList(Collection<S> items, Class<T> elementType) {
066 return items.stream()
067 .map(elementType::cast)
068 .toList();
069 }
070
071 /**
072 * Creates a copy of array.
073 *
074 * @param array Array to create a copy of
075 * @param length length of array
076 * @param <T> The type of array
077 * @return copy of array
078 */
079 public static <T> T[] copyOfArray(T[] array, int length) {
080 return Arrays.copyOf(array, length);
081 }
082
083 /**
084 * Creates a copy of Map.
085 *
086 * @param map map to create a copy of
087 * @param <K> the type of keys in the map
088 * @param <V> the type of values in the map
089 * @return an immutable copy of the input map
090 */
091 public static <K, V> Map<K, V> copyOfMap(Map<? extends K, ? extends V> map) {
092 return Map.copyOf(map);
093 }
094
095 /**
096 * Returns an immutable set containing only the specified object.
097 *
098 * @param obj the type of object in the set
099 * @param <T> the type of object
100 * @return immutable set
101 */
102 public static <T> Set<T> singleton(T obj) {
103 return Collections.singleton(obj);
104 }
105}