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}