001/////////////////////////////////////////////////////////////////////////////////////////////// 002// checkstyle: Checks Java source code and other text files for adherence to a set of rules. 003// Copyright (C) 2001-2024 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; 028import java.util.stream.Collectors; 029 030/** 031 * <div>Note: it simply wraps the existing JDK methods to provide a workaround 032 * for Pitest survival on mutation for removal of immutable wrapping, 033 * see #13127 for more details. 034 * </div> 035 * 036 */ 037public final class UnmodifiableCollectionUtil { 038 039 /** 040 * Private constructor for UnmodifiableCollectionUtil. 041 * 042 */ 043 private UnmodifiableCollectionUtil() { 044 } 045 046 /** 047 * Creates an unmodifiable list based on the provided collection. 048 * 049 * @param collection the collection to create an unmodifiable list from 050 * @param <T> the type of elements in the set 051 * @return an unmodifiable list containing the elements from the provided collection 052 */ 053 public static <T> List<T> unmodifiableList(List<T> collection) { 054 return Collections.unmodifiableList(collection); 055 } 056 057 /** 058 * Returns an unmodifiable view of a List containing elements of a specific type. 059 * 060 * @param items The List of items to make unmodifiable. 061 * @param elementType The Class object representing the type of elements in the list. 062 * @param <S> The generic type of elements in the input Collection. 063 * @param <T> The type of elements in the resulting unmodifiable List. 064 * @return An unmodifiable List containing elements of the specified type. 065 */ 066 public static <S, T> List<T> unmodifiableList(Collection<S> items, Class<T> elementType) { 067 return items.stream() 068 .map(elementType::cast) 069 .collect(Collectors.toUnmodifiableList()); 070 } 071 072 /** 073 * Creates a copy of array. 074 * 075 * @param array Array to create a copy of 076 * @param length length of array 077 * @param <T> The type of array 078 * @return copy of array 079 */ 080 public static <T> T[] copyOfArray(T[] array, int length) { 081 return Arrays.copyOf(array, length); 082 } 083 084 /** 085 * Creates a copy of Map. 086 * 087 * @param map map to create a copy of 088 * @param <K> the type of keys in the map 089 * @param <V> the type of values in the map 090 * @return an immutable copy of the input map 091 */ 092 public static <K, V> Map<K, V> copyOfMap(Map<? extends K, ? extends V> map) { 093 return Map.copyOf(map); 094 } 095 096 /** 097 * Returns an immutable set containing only the specified object. 098 * 099 * @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}