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| 1 | /* | ||
| 2 | * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * This class consists of {@code static} utility methods for operating | ||
| 30 | * on objects. These utilities include {@code null}-safe or {@code | ||
| 31 | * null}-tolerant methods for computing the hash code of an object, | ||
| 32 | * returning a string for an object, and comparing two objects. | ||
| 33 | * | ||
| 34 | * @since 1.7 | ||
| 35 | */ | ||
| 36 | public final class Objects { | ||
| 37 | private Objects() { | ||
| 38 | throw new AssertionError("No java.util.Objects instances for you!"); | ||
| 39 | } | ||
| 40 | |||
| 41 | /** | ||
| 42 | * Returns {@code true} if the arguments are equal to each other | ||
| 43 | * and {@code false} otherwise. | ||
| 44 | * Consequently, if both arguments are {@code null}, {@code true} | ||
| 45 | * is returned and if exactly one argument is {@code null}, {@code | ||
| 46 | * false} is returned. Otherwise, equality is determined by using | ||
| 47 | * the {@link Object#equals equals} method of the first | ||
| 48 | * argument. | ||
| 49 | * | ||
| 50 | * @param a an object | ||
| 51 | * @param b an object to be compared with {@code a} for equality | ||
| 52 | * @return {@code true} if the arguments are equal to each other | ||
| 53 | * and {@code false} otherwise | ||
| 54 | * @see Object#equals(Object) | ||
| 55 | */ | ||
| 56 | public static boolean equals(Object a, Object b) { | ||
| 57 | return (a == b) || (a != null && a.equals(b)); | ||
| 58 | } | ||
| 59 | |||
| 60 | /** | ||
| 61 | * Returns {@code true} if the arguments are deeply equal to each other | ||
| 62 | * and {@code false} otherwise. | ||
| 63 | * | ||
| 64 | * Two {@code null} values are deeply equal. If both arguments are | ||
| 65 | * arrays, the algorithm in {@link Arrays#deepEquals(Object[], | ||
| 66 | * Object[]) Arrays.deepEquals} is used to determine equality. | ||
| 67 | * Otherwise, equality is determined by using the {@link | ||
| 68 | * Object#equals equals} method of the first argument. | ||
| 69 | * | ||
| 70 | * @param a an object | ||
| 71 | * @param b an object to be compared with {@code a} for deep equality | ||
| 72 | * @return {@code true} if the arguments are deeply equal to each other | ||
| 73 | * and {@code false} otherwise | ||
| 74 | * @see Arrays#deepEquals(Object[], Object[]) | ||
| 75 | * @see Objects#equals(Object, Object) | ||
| 76 | */ | ||
| 77 | public static boolean deepEquals(Object a, Object b) { | ||
| 78 | if (a == b) | ||
| 79 | return true; | ||
| 80 | else if (a == null || b == null) | ||
| 81 | return false; | ||
| 82 | else | ||
| 83 | return Arrays.deepEquals0(a, b); | ||
| 84 | } | ||
| 85 | |||
| 86 | /** | ||
| 87 | * Returns the hash code of a non-{@code null} argument and 0 for | ||
| 88 | * a {@code null} argument. | ||
| 89 | * | ||
| 90 | * @param o an object | ||
| 91 | * @return the hash code of a non-{@code null} argument and 0 for | ||
| 92 | * a {@code null} argument | ||
| 93 | * @see Object#hashCode | ||
| 94 | */ | ||
| 95 | public static int hashCode(Object o) { | ||
| 96 | return o != null ? o.hashCode() : 0; | ||
| 97 | } | ||
| 98 | |||
| 99 | /** | ||
| 100 | * Generates a hash code for a sequence of input values. The hash | ||
| 101 | * code is generated as if all the input values were placed into an | ||
| 102 | * array, and that array were hashed by calling {@link | ||
| 103 | * Arrays#hashCode(Object[])}. | ||
| 104 | * | ||
| 105 | * <p>This method is useful for implementing {@link | ||
| 106 | * Object#hashCode()} on objects containing multiple fields. For | ||
| 107 | * example, if an object that has three fields, {@code x}, {@code | ||
| 108 | * y}, and {@code z}, one could write: | ||
| 109 | * | ||
| 110 | * <blockquote><pre> | ||
| 111 | * @Override public int hashCode() { | ||
| 112 | * return Objects.hash(x, y, z); | ||
| 113 | * } | ||
| 114 | * </pre></blockquote> | ||
| 115 | * | ||
| 116 | * <b>Warning: When a single object reference is supplied, the returned | ||
| 117 | * value does not equal the hash code of that object reference.</b> This | ||
| 118 | * value can be computed by calling {@link #hashCode(Object)}. | ||
| 119 | * | ||
| 120 | * @param values the values to be hashed | ||
| 121 | * @return a hash value of the sequence of input values | ||
| 122 | * @see Arrays#hashCode(Object[]) | ||
| 123 | * @see List#hashCode | ||
| 124 | */ | ||
| 125 | public static int hash(Object... values) { | ||
| 126 | return Arrays.hashCode(values); | ||
| 127 | } | ||
| 128 | |||
| 129 | /** | ||
| 130 | * Returns the result of calling {@code toString} for a non-{@code | ||
| 131 | * null} argument and {@code "null"} for a {@code null} argument. | ||
| 132 | * | ||
| 133 | * @param o an object | ||
| 134 | * @return the result of calling {@code toString} for a non-{@code | ||
| 135 | * null} argument and {@code "null"} for a {@code null} argument | ||
| 136 | * @see Object#toString | ||
| 137 | * @see String#valueOf(Object) | ||
| 138 | */ | ||
| 139 | public static String toString(Object o) { | ||
| 140 | return String.valueOf(o); | ||
| 141 | } | ||
| 142 | |||
| 143 | /** | ||
| 144 | * Returns the result of calling {@code toString} on the first | ||
| 145 | * argument if the first argument is not {@code null} and returns | ||
| 146 | * the second argument otherwise. | ||
| 147 | * | ||
| 148 | * @param o an object | ||
| 149 | * @param nullDefault string to return if the first argument is | ||
| 150 | * {@code null} | ||
| 151 | * @return the result of calling {@code toString} on the first | ||
| 152 | * argument if it is not {@code null} and the second argument | ||
| 153 | * otherwise. | ||
| 154 | * @see Objects#toString(Object) | ||
| 155 | */ | ||
| 156 | public static String toString(Object o, String nullDefault) { | ||
| 157 | return (o != null) ? o.toString() : nullDefault; | ||
| 158 | } | ||
| 159 | |||
| 160 | /** | ||
| 161 | * Returns 0 if the arguments are identical and {@code | ||
| 162 | * c.compare(a, b)} otherwise. | ||
| 163 | * Consequently, if both arguments are {@code null} 0 | ||
| 164 | * is returned. | ||
| 165 | * | ||
| 166 | * <p>Note that if one of the arguments is {@code null}, a {@code | ||
| 167 | * NullPointerException} may or may not be thrown depending on | ||
| 168 | * what ordering policy, if any, the {@link Comparator Comparator} | ||
| 169 | * chooses to have for {@code null} values. | ||
| 170 | * | ||
| 171 | * @param <T> the type of the objects being compared | ||
| 172 | * @param a an object | ||
| 173 | * @param b an object to be compared with {@code a} | ||
| 174 | * @param c the {@code Comparator} to compare the first two arguments | ||
| 175 | * @return 0 if the arguments are identical and {@code | ||
| 176 | * c.compare(a, b)} otherwise. | ||
| 177 | * @see Comparable | ||
| 178 | * @see Comparator | ||
| 179 | */ | ||
| 180 | public static <T> int compare(T a, T b, Comparator<? super T> c) { | ||
| 181 | return (a == b) ? 0 : c.compare(a, b); | ||
| 182 | } | ||
| 183 | |||
| 184 | /** | ||
| 185 | * Checks that the specified object reference is not {@code null}. This | ||
| 186 | * method is designed primarily for doing parameter validation in methods | ||
| 187 | * and constructors, as demonstrated below: | ||
| 188 | * <blockquote><pre> | ||
| 189 | * public Foo(Bar bar) { | ||
| 190 | * this.bar = Objects.requireNonNull(bar); | ||
| 191 | * } | ||
| 192 | * </pre></blockquote> | ||
| 193 | * | ||
| 194 | * @param obj the object reference to check for nullity | ||
| 195 | * @param <T> the type of the reference | ||
| 196 | * @return {@code obj} if not {@code null} | ||
| 197 | * @throws NullPointerException if {@code obj} is {@code null} | ||
| 198 | */ | ||
| 199 | public static <T> T requireNonNull(T obj) { | ||
| 200 | if (obj == null) | ||
| 201 | throw new NullPointerException(); | ||
| 202 | return obj; | ||
| 203 | } | ||
| 204 | |||
| 205 | /** | ||
| 206 | * Checks that the specified object reference is not {@code null} and | ||
| 207 | * throws a customized {@link NullPointerException} if it is. This method | ||
| 208 | * is designed primarily for doing parameter validation in methods and | ||
| 209 | * constructors with multiple parameters, as demonstrated below: | ||
| 210 | * <blockquote><pre> | ||
| 211 | * public Foo(Bar bar, Baz baz) { | ||
| 212 | * this.bar = Objects.requireNonNull(bar, "bar must not be null"); | ||
| 213 | * this.baz = Objects.requireNonNull(baz, "baz must not be null"); | ||
| 214 | * } | ||
| 215 | * </pre></blockquote> | ||
| 216 | * | ||
| 217 | * @param obj the object reference to check for nullity | ||
| 218 | * @param message detail message to be used in the event that a {@code | ||
| 219 | * NullPointerException} is thrown | ||
| 220 | * @param <T> the type of the reference | ||
| 221 | * @return {@code obj} if not {@code null} | ||
| 222 | * @throws NullPointerException if {@code obj} is {@code null} | ||
| 223 | */ | ||
| 224 | public static <T> T requireNonNull(T obj, String message) { | ||
| 225 | if (obj == null) | ||
| 226 | throw new NullPointerException(message); | ||
| 227 | return obj; | ||
| 228 | } | ||
| 229 | } | ||