1 /*
2 * Copyright 2009 Sun Microsystems, Inc. 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. Sun designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 * CA 95054 USA or visit www.sun.com if you need additional information or
23 * have any 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
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.nonNull(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 nonNull(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.nonNull(bar, "bar must not be null");
213 * this.baz = Objects.nonNull(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 nonNull(T obj, String message) {
225 if (obj == null)
226 throw new NullPointerException(message);
227 return obj;
228 }
229 }