1 /*
2 * Copyright (c) 2009, 2016, 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 import jdk.internal.util.Preconditions;
29 import jdk.internal.vm.annotation.ForceInline;
30
31 import java.util.function.Supplier;
32
33 /**
34 * This class consists of {@code static} utility methods for operating
35 * on objects, or checking certain conditions before operation. These utilities
36 * include {@code null}-safe or {@code null}-tolerant methods for computing the
37 * hash code of an object, returning a string for an object, comparing two
38 * objects, and checking if indexes or sub-range values are out-of-bounds.
39 *
40 * @apiNote
41 * Static methods such as {@link Objects#checkIndex},
42 * {@link Objects#checkFromToIndex}, and {@link Objects#checkFromIndexSize} are
43 * provided for the convenience of checking if values corresponding to indexes
44 * and sub-ranges are out-of-bounds.
45 * Variations of these static methods support customization of the runtime
46 * exception, and corresponding exception detail message, that is thrown when
47 * values are out-of-bounds. Such methods accept a functional interface
48 * argument, instances of {@code BiFunction}, that maps out-of-bound values to a
49 * runtime exception. Care should be taken when using such methods in
50 * combination with an argument that is a lambda expression, method reference or
51 * class that capture values. In such cases the cost of capture, related to
52 * functional interface allocation, may exceed the cost of checking bounds.
53 *
54 * @since 1.7
55 */
56 public final class Objects {
57 private Objects() {
58 throw new AssertionError("No java.util.Objects instances for you!");
59 }
60
61 /**
62 * Returns {@code true} if the arguments are equal to each other
63 * and {@code false} otherwise.
64 * Consequently, if both arguments are {@code null}, {@code true}
65 * is returned and if exactly one argument is {@code null}, {@code
66 * false} is returned. Otherwise, equality is determined by using
67 * the {@link Object#equals equals} method of the first
68 * argument.
69 *
70 * @param a an object
71 * @param b an object to be compared with {@code a} for equality
72 * @return {@code true} if the arguments are equal to each other
73 * and {@code false} otherwise
74 * @see Object#equals(Object)
75 */
76 public static boolean equals(Object a, Object b) {
77 return (a == b) || (a != null && a.equals(b));
78 }
79
80 /**
81 * Returns {@code true} if the arguments are deeply equal to each other
82 * and {@code false} otherwise.
83 *
84 * Two {@code null} values are deeply equal. If both arguments are
85 * arrays, the algorithm in {@link Arrays#deepEquals(Object[],
86 * Object[]) Arrays.deepEquals} is used to determine equality.
87 * Otherwise, equality is determined by using the {@link
88 * Object#equals equals} method of the first argument.
89 *
90 * @param a an object
91 * @param b an object to be compared with {@code a} for deep equality
92 * @return {@code true} if the arguments are deeply equal to each other
93 * and {@code false} otherwise
94 * @see Arrays#deepEquals(Object[], Object[])
95 * @see Objects#equals(Object, Object)
96 */
97 public static boolean deepEquals(Object a, Object b) {
98 if (a == b)
99 return true;
100 else if (a == null || b == null)
101 return false;
102 else
103 return Arrays.deepEquals0(a, b);
104 }
105
106 /**
107 * Returns the hash code of a non-{@code null} argument and 0 for
108 * a {@code null} argument.
109 *
110 * @param o an object
111 * @return the hash code of a non-{@code null} argument and 0 for
112 * a {@code null} argument
113 * @see Object#hashCode
114 */
115 public static int hashCode(Object o) {
116 return o != null ? o.hashCode() : 0;
117 }
118
119 /**
120 * Generates a hash code for a sequence of input values. The hash
121 * code is generated as if all the input values were placed into an
122 * array, and that array were hashed by calling {@link
123 * Arrays#hashCode(Object[])}.
124 *
125 * <p>This method is useful for implementing {@link
126 * Object#hashCode()} on objects containing multiple fields. For
127 * example, if an object that has three fields, {@code x}, {@code
128 * y}, and {@code z}, one could write:
129 *
130 * <blockquote><pre>
131 * @Override public int hashCode() {
132 * return Objects.hash(x, y, z);
133 * }
134 * </pre></blockquote>
135 *
136 * <b>Warning: When a single object reference is supplied, the returned
137 * value does not equal the hash code of that object reference.</b> This
138 * value can be computed by calling {@link #hashCode(Object)}.
139 *
140 * @param values the values to be hashed
141 * @return a hash value of the sequence of input values
142 * @see Arrays#hashCode(Object[])
143 * @see List#hashCode
144 */
145 public static int hash(Object... values) {
146 return Arrays.hashCode(values);
147 }
148
149 /**
150 * Returns the result of calling {@code toString} for a non-{@code
151 * null} argument and {@code "null"} for a {@code null} argument.
152 *
153 * @param o an object
154 * @return the result of calling {@code toString} for a non-{@code
155 * null} argument and {@code "null"} for a {@code null} argument
156 * @see Object#toString
157 * @see String#valueOf(Object)
158 */
159 public static String toString(Object o) {
160 return String.valueOf(o);
161 }
162
163 /**
164 * Returns the result of calling {@code toString} on the first
165 * argument if the first argument is not {@code null} and returns
166 * the second argument otherwise.
167 *
168 * @param o an object
169 * @param nullDefault string to return if the first argument is
170 * {@code null}
171 * @return the result of calling {@code toString} on the first
172 * argument if it is not {@code null} and the second argument
173 * otherwise.
174 * @see Objects#toString(Object)
175 */
176 public static String toString(Object o, String nullDefault) {
177 return (o != null) ? o.toString() : nullDefault;
178 }
179
180 /**
181 * Returns 0 if the arguments are identical and {@code
182 * c.compare(a, b)} otherwise.
183 * Consequently, if both arguments are {@code null} 0
184 * is returned.
185 *
186 * <p>Note that if one of the arguments is {@code null}, a {@code
187 * NullPointerException} may or may not be thrown depending on
188 * what ordering policy, if any, the {@link Comparator Comparator}
189 * chooses to have for {@code null} values.
190 *
191 * @param <T> the type of the objects being compared
192 * @param a an object
193 * @param b an object to be compared with {@code a}
194 * @param c the {@code Comparator} to compare the first two arguments
195 * @return 0 if the arguments are identical and {@code
196 * c.compare(a, b)} otherwise.
197 * @see Comparable
198 * @see Comparator
199 */
200 public static <T> int compare(T a, T b, Comparator<? super T> c) {
201 return (a == b) ? 0 : c.compare(a, b);
202 }
203
204 /**
205 * Checks that the specified object reference is not {@code null}. This
206 * method is designed primarily for doing parameter validation in methods
207 * and constructors, as demonstrated below:
208 * <blockquote><pre>
209 * public Foo(Bar bar) {
210 * this.bar = Objects.requireNonNull(bar);
211 * }
212 * </pre></blockquote>
213 *
214 * @param obj the object reference to check for nullity
215 * @param <T> the type of the reference
216 * @return {@code obj} if not {@code null}
217 * @throws NullPointerException if {@code obj} is {@code null}
218 */
219 public static <T> T requireNonNull(T obj) {
220 if (obj == null)
221 throw new NullPointerException();
222 return obj;
223 }
224
225 /**
226 * Checks that the specified object reference is not {@code null} and
227 * throws a customized {@link NullPointerException} if it is. This method
228 * is designed primarily for doing parameter validation in methods and
229 * constructors with multiple parameters, as demonstrated below:
230 * <blockquote><pre>
231 * public Foo(Bar bar, Baz baz) {
232 * this.bar = Objects.requireNonNull(bar, "bar must not be null");
233 * this.baz = Objects.requireNonNull(baz, "baz must not be null");
234 * }
235 * </pre></blockquote>
236 *
237 * @param obj the object reference to check for nullity
238 * @param message detail message to be used in the event that a {@code
239 * NullPointerException} is thrown
240 * @param <T> the type of the reference
241 * @return {@code obj} if not {@code null}
242 * @throws NullPointerException if {@code obj} is {@code null}
243 */
244 public static <T> T requireNonNull(T obj, String message) {
245 if (obj == null)
246 throw new NullPointerException(message);
247 return obj;
248 }
249
250 /**
251 * Returns {@code true} if the provided reference is {@code null} otherwise
252 * returns {@code false}.
253 *
254 * @apiNote This method exists to be used as a
255 * {@link java.util.function.Predicate}, {@code filter(Objects::isNull)}
256 *
257 * @param obj a reference to be checked against {@code null}
258 * @return {@code true} if the provided reference is {@code null} otherwise
259 * {@code false}
260 *
261 * @see java.util.function.Predicate
262 * @since 1.8
263 */
264 public static boolean isNull(Object obj) {
265 return obj == null;
266 }
267
268 /**
269 * Returns {@code true} if the provided reference is non-{@code null}
270 * otherwise returns {@code false}.
271 *
272 * @apiNote This method exists to be used as a
273 * {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)}
274 *
275 * @param obj a reference to be checked against {@code null}
276 * @return {@code true} if the provided reference is non-{@code null}
277 * otherwise {@code false}
278 *
279 * @see java.util.function.Predicate
280 * @since 1.8
281 */
282 public static boolean nonNull(Object obj) {
283 return obj != null;
284 }
285
286 /**
287 * Returns the first argument if it is non-{@code null} and
288 * otherwise returns the non-{@code null} second argument.
289 *
290 * @param obj an object
291 * @param defaultObj a non-{@code null} object to return if the first argument
292 * is {@code null}
293 * @param <T> the type of the reference
294 * @return the first argument if it is non-{@code null} and
295 * otherwise the second argument if it is non-{@code null}
296 * @throws NullPointerException if both {@code obj} is null and
297 * {@code defaultObj} is {@code null}
298 * @since 9
299 */
300 public static <T> T requireNonNullElse(T obj, T defaultObj) {
301 return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
302 }
303
304 /**
305 * Returns the first argument if it is non-{@code null} and otherwise
306 * returns the non-{@code null} value of {@code supplier.get()}.
307 *
308 * @param obj an object
309 * @param supplier of a non-{@code null} object to return if the first argument
310 * is {@code null}
311 * @param <T> the type of the first argument and return type
312 * @return the first argument if it is non-{@code null} and otherwise
313 * the value from {@code supplier.get()} if it is non-{@code null}
314 * @throws NullPointerException if both {@code obj} is null and
315 * either the {@code supplier} is {@code null} or
316 * the {@code supplier.get()} value is {@code null}
317 * @since 9
318 */
319 public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
320 return (obj != null) ? obj
321 : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
322 }
323
324 /**
325 * Checks that the specified object reference is not {@code null} and
326 * throws a customized {@link NullPointerException} if it is.
327 *
328 * <p>Unlike the method {@link #requireNonNull(Object, String)},
329 * this method allows creation of the message to be deferred until
330 * after the null check is made. While this may confer a
331 * performance advantage in the non-null case, when deciding to
332 * call this method care should be taken that the costs of
333 * creating the message supplier are less than the cost of just
334 * creating the string message directly.
335 *
336 * @param obj the object reference to check for nullity
337 * @param messageSupplier supplier of the detail message to be
338 * used in the event that a {@code NullPointerException} is thrown
339 * @param <T> the type of the reference
340 * @return {@code obj} if not {@code null}
341 * @throws NullPointerException if {@code obj} is {@code null}
342 * @since 1.8
343 */
344 public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
345 if (obj == null)
346 throw new NullPointerException(messageSupplier == null ?
347 null : messageSupplier.get());
348 return obj;
349 }
350
351 /**
352 * Checks if the {@code index} is within the bounds of the range from
353 * {@code 0} (inclusive) to {@code length} (exclusive).
354 *
355 * <p>The {@code index} is defined to be out-of-bounds if any of the
356 * following inequalities is true:
357 * <ul>
358 * <li>{@code index < 0}</li>
359 * <li>{@code index >= length}</li>
360 * <li>{@code length < 0}, which is implied from the former inequalities</li>
361 * </ul>
362 *
363 * @param index the index
364 * @param length the upper-bound (exclusive) of the range
365 * @return {@code index} if it is within bounds of the range
366 * @throws IndexOutOfBoundsException if the {@code index} is out-of-bounds
367 * @since 9
368 */
369 @ForceInline
370 public static
371 int checkIndex(int index, int length) {
372 return Preconditions.checkIndex(index, length, null);
373 }
374
375 /**
376 * Checks if the sub-range from {@code fromIndex} (inclusive) to
377 * {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
378 * (inclusive) to {@code length} (exclusive).
379 *
380 * <p>The sub-range is defined to be out-of-bounds if any of the following
381 * inequalities is true:
382 * <ul>
383 * <li>{@code fromIndex < 0}</li>
384 * <li>{@code fromIndex > toIndex}</li>
385 * <li>{@code toIndex > length}</li>
386 * <li>{@code length < 0}, which is implied from the former inequalities</li>
387 * </ul>
388 *
389 * @param fromIndex the lower-bound (inclusive) of the sub-range
390 * @param toIndex the upper-bound (exclusive) of the sub-range
391 * @param length the upper-bound (exclusive) the range
392 * @return {@code fromIndex} if the sub-range within bounds of the range
393 * @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
394 * @since 9
395 */
396 public static
397 int checkFromToIndex(int fromIndex, int toIndex, int length) {
398 return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
399 }
400
401 /**
402 * Checks if the sub-range from {@code fromIndex} (inclusive) to
403 * {@code fromIndex + size} (exclusive) is within the bounds of range from
404 * {@code 0} (inclusive) to {@code length} (exclusive).
405 *
406 * <p>The sub-range is defined to be out-of-bounds if any of the following
407 * inequalities is true:
408 * <ul>
409 * <li>{@code fromIndex < 0}</li>
410 * <li>{@code size < 0}</li>
411 * <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
412 * <li>{@code length < 0}, which is implied from the former inequalities</li>
413 * </ul>
414 *
415 * @param fromIndex the lower-bound (inclusive) of the sub-interval
416 * @param size the size of the sub-range
417 * @param length the upper-bound (exclusive) of the range
418 * @return {@code fromIndex} if the sub-range within bounds of the range
419 * @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
420 * @since 9
421 */
422 public static
423 int checkFromIndexSize(int fromIndex, int size, int length) {
424 return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
425 }
426
427 }