1 ///////////////////////////////////////////////////////////////////////////////////////////////
2 // checkstyle: Checks Java source code and other text files for adherence to a set of rules.
3 // Copyright (C) 2001-2024 the original author or authors.
4 //
5 // This library is free software; you can redistribute it and/or
6 // modify it under the terms of the GNU Lesser General Public
7 // License as published by the Free Software Foundation; either
8 // version 2.1 of the License, or (at your option) any later version.
9 //
10 // This library is distributed in the hope that it will be useful,
11 // but WITHOUT ANY WARRANTY; without even the implied warranty of
12 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
13 // Lesser General Public License for more details.
14 //
15 // You should have received a copy of the GNU Lesser General Public
16 // License along with this library; if not, write to the Free Software
17 // Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
18 ///////////////////////////////////////////////////////////////////////////////////////////////
19
20 package com.puppycrawl.tools.checkstyle.utils;
21
22 import java.util.Arrays;
23 import java.util.Collection;
24 import java.util.Collections;
25 import java.util.List;
26 import java.util.Map;
27 import java.util.Set;
28 import java.util.stream.Collectors;
29
30 /**
31 * <div>Note: it simply wraps the existing JDK methods to provide a workaround
32 * for Pitest survival on mutation for removal of immutable wrapping,
33 * see #13127 for more details.
34 * </div>
35 *
36 */
37 public final class UnmodifiableCollectionUtil {
38
39 /**
40 * Private constructor for UnmodifiableCollectionUtil.
41 *
42 */
43 private UnmodifiableCollectionUtil() {
44 }
45
46 /**
47 * Creates an unmodifiable list based on the provided collection.
48 *
49 * @param collection the collection to create an unmodifiable list from
50 * @param <T> the type of elements in the set
51 * @return an unmodifiable list containing the elements from the provided collection
52 */
53 public static <T> List<T> unmodifiableList(List<T> collection) {
54 return Collections.unmodifiableList(collection);
55 }
56
57 /**
58 * Returns an unmodifiable view of a List containing elements of a specific type.
59 *
60 * @param items The List of items to make unmodifiable.
61 * @param elementType The Class object representing the type of elements in the list.
62 * @param <S> The generic type of elements in the input Collection.
63 * @param <T> The type of elements in the resulting unmodifiable List.
64 * @return An unmodifiable List containing elements of the specified type.
65 */
66 public static <S, T> List<T> unmodifiableList(Collection<S> items, Class<T> elementType) {
67 return items.stream()
68 .map(elementType::cast)
69 .collect(Collectors.toUnmodifiableList());
70 }
71
72 /**
73 * Creates a copy of array.
74 *
75 * @param array Array to create a copy of
76 * @param length length of array
77 * @param <T> The type of array
78 * @return copy of array
79 */
80 public static <T> T[] copyOfArray(T[] array, int length) {
81 return Arrays.copyOf(array, length);
82 }
83
84 /**
85 * Creates a copy of Map.
86 *
87 * @param map map to create a copy of
88 * @param <K> the type of keys in the map
89 * @param <V> the type of values in the map
90 * @return an immutable copy of the input map
91 */
92 public static <K, V> Map<K, V> copyOfMap(Map<? extends K, ? extends V> map) {
93 return Map.copyOf(map);
94 }
95
96 /**
97 * Returns an immutable set containing only the specified object.
98 *
99 * @param obj the type of object in the set
100 * @param <T> the type of object
101 * @return immutable set
102 */
103 public static <T> Set<T> singleton(T obj) {
104 return Collections.singleton(obj);
105 }
106 }