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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 | +} | |