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 import jdk.internal.misc.Unsafe;
31
32 import java.util.function.Supplier;
33
34 /**
35 * This class consists of {@code static} utility methods for operating
36 * on objects, or checking certain conditions before operation. These utilities
37 * include {@code null}-safe or {@code null}-tolerant methods for computing the
38 * hash code of an object, returning a string for an object, comparing two
39 * objects, and checking if indexes or sub-range values are out of bounds.
40 *
41 * @apiNote
42 * Static methods such as {@link Objects#checkIndex},
43 * {@link Objects#checkFromToIndex}, and {@link Objects#checkFromIndexSize} are
44 * provided for the convenience of checking if values corresponding to indexes
45 * and sub-ranges are out of bounds.
46 * Variations of these static methods support customization of the runtime
47 * exception, and corresponding exception detail message, that is thrown when
48 * values are out of bounds. Such methods accept a functional interface
49 * argument, instances of {@code BiFunction}, that maps out-of-bound values to a
50 * runtime exception. Care should be taken when using such methods in
51 * combination with an argument that is a lambda expression, method reference or
52 * class that capture values. In such cases the cost of capture, related to
53 * functional interface allocation, may exceed the cost of checking bounds.
54 *
55 * @since 1.7
56 */
57 public final class Objects {
58 private Objects() {
59 throw new AssertionError("No java.util.Objects instances for you!");
60 }
61
62 /**
63 * Returns {@code true} if the arguments are equal to each other
64 * and {@code false} otherwise.
65 * Consequently, if both arguments are {@code null}, {@code true}
66 * is returned. Otherwise, if the first argument is not {@code
67 * null}, equality is determined by calling the {@link
68 * Object#equals equals} method of the first argument with the
69 * second argument of this method. Otherwise, {@code false} is
70 * returned.
71 *
72 * @param a an object
73 * @param b an object to be compared with {@code a} for equality
74 * @return {@code true} if the arguments are equal to each other
75 * and {@code false} otherwise
76 * @see Object#equals(Object)
77 */
78 public static boolean equals(Object a, Object b) {
79 return (a == b) || (a != null && a.equals(b));
80 }
81
82 /**
83 * Returns {@code true} if the arguments are deeply equal to each other
84 * and {@code false} otherwise.
85 *
86 * Two {@code null} values are deeply equal. If both arguments are
87 * arrays, the algorithm in {@link Arrays#deepEquals(Object[],
88 * Object[]) Arrays.deepEquals} is used to determine equality.
89 * Otherwise, equality is determined by using the {@link
90 * Object#equals equals} method of the first argument.
91 *
92 * @param a an object
93 * @param b an object to be compared with {@code a} for deep equality
94 * @return {@code true} if the arguments are deeply equal to each other
95 * and {@code false} otherwise
96 * @see Arrays#deepEquals(Object[], Object[])
97 * @see Objects#equals(Object, Object)
98 */
99 public static boolean deepEquals(Object a, Object b) {
100 if (a == b)
101 return true;
102 else if (a == null || b == null)
103 return false;
104 else
105 return Arrays.deepEquals0(a, b);
106 }
107
108 /**
109 * Returns the hash code of a non-{@code null} argument and 0 for
110 * a {@code null} argument.
111 *
112 * @param o an object
113 * @return the hash code of a non-{@code null} argument and 0 for
114 * a {@code null} argument
115 * @see Object#hashCode
116 */
117 public static int hashCode(Object o) {
118 return o != null ? o.hashCode() : 0;
119 }
120
121 /**
122 * Generates a hash code for a sequence of input values. The hash
123 * code is generated as if all the input values were placed into an
124 * array, and that array were hashed by calling {@link
125 * Arrays#hashCode(Object[])}.
126 *
127 * <p>This method is useful for implementing {@link
128 * Object#hashCode()} on objects containing multiple fields. For
129 * example, if an object that has three fields, {@code x}, {@code
130 * y}, and {@code z}, one could write:
131 *
132 * <blockquote><pre>
133 * @Override public int hashCode() {
134 * return Objects.hash(x, y, z);
135 * }
136 * </pre></blockquote>
137 *
138 * <b>Warning: When a single object reference is supplied, the returned
139 * value does not equal the hash code of that object reference.</b> This
140 * value can be computed by calling {@link #hashCode(Object)}.
141 *
142 * @param values the values to be hashed
143 * @return a hash value of the sequence of input values
144 * @see Arrays#hashCode(Object[])
145 * @see List#hashCode
146 */
147 public static int hash(Object... values) {
148 return Arrays.hashCode(values);
149 }
150
151 /**
152 * Returns the result of calling {@code toString} for a non-{@code
153 * null} argument and {@code "null"} for a {@code null} argument.
154 *
155 * @param o an object
156 * @return the result of calling {@code toString} for a non-{@code
157 * null} argument and {@code "null"} for a {@code null} argument
158 * @see Object#toString
159 * @see String#valueOf(Object)
160 */
161 public static String toString(Object o) {
162 return String.valueOf(o);
163 }
164
165 /**
166 * Returns the result of calling {@code toString} on the first
167 * argument if the first argument is not {@code null} and returns
168 * the second argument otherwise.
169 *
170 * @param o an object
171 * @param nullDefault string to return if the first argument is
172 * {@code null}
173 * @return the result of calling {@code toString} on the first
174 * argument if it is not {@code null} and the second argument
175 * otherwise.
176 * @see Objects#toString(Object)
177 */
178 public static String toString(Object o, String nullDefault) {
179 return (o != null) ? o.toString() : nullDefault;
180 }
181
182 /**
183 * Returns 0 if the arguments are identical and {@code
184 * c.compare(a, b)} otherwise.
185 * Consequently, if both arguments are {@code null} 0
186 * is returned.
187 *
188 * <p>Note that if one of the arguments is {@code null}, a {@code
189 * NullPointerException} may or may not be thrown depending on
190 * what ordering policy, if any, the {@link Comparator Comparator}
191 * chooses to have for {@code null} values.
192 *
193 * @param <T> the type of the objects being compared
194 * @param a an object
195 * @param b an object to be compared with {@code a}
196 * @param c the {@code Comparator} to compare the first two arguments
197 * @return 0 if the arguments are identical and {@code
198 * c.compare(a, b)} otherwise.
199 * @see Comparable
200 * @see Comparator
201 */
202 public static <T> int compare(T a, T b, Comparator<? super T> c) {
203 return (a == b) ? 0 : c.compare(a, b);
204 }
205
206 /**
207 * Checks that the specified object reference is not {@code null}. This
208 * method is designed primarily for doing parameter validation in methods
209 * and constructors, as demonstrated below:
210 * <blockquote><pre>
211 * public Foo(Bar bar) {
212 * this.bar = Objects.requireNonNull(bar);
213 * }
214 * </pre></blockquote>
215 *
216 * @param obj the object reference to check for nullity
217 * @param <T> the type of the reference
218 * @return {@code obj} if not {@code null}
219 * @throws NullPointerException if {@code obj} is {@code null}
220 */
221 public static <T> T requireNonNull(T obj) {
222 if (obj == null)
223 throw new NullPointerException();
224 return obj;
225 }
226
227 /**
228 * Checks that the specified object reference is not {@code null} and
229 * throws a customized {@link NullPointerException} if it is. This method
230 * is designed primarily for doing parameter validation in methods and
231 * constructors with multiple parameters, as demonstrated below:
232 * <blockquote><pre>
233 * public Foo(Bar bar, Baz baz) {
234 * this.bar = Objects.requireNonNull(bar, "bar must not be null");
235 * this.baz = Objects.requireNonNull(baz, "baz must not be null");
236 * }
237 * </pre></blockquote>
238 *
239 * @param obj the object reference to check for nullity
240 * @param message detail message to be used in the event that a {@code
241 * NullPointerException} is thrown
242 * @param <T> the type of the reference
243 * @return {@code obj} if not {@code null}
244 * @throws NullPointerException if {@code obj} is {@code null}
245 */
246 public static <T> T requireNonNull(T obj, String message) {
247 if (obj == null)
248 throw new NullPointerException(message);
249 return obj;
250 }
251
252 /**
253 * Returns {@code true} if the provided reference is {@code null} otherwise
254 * returns {@code false}.
255 *
256 * @apiNote This method exists to be used as a
257 * {@link java.util.function.Predicate}, {@code filter(Objects::isNull)}
258 *
259 * @param obj a reference to be checked against {@code null}
260 * @return {@code true} if the provided reference is {@code null} otherwise
261 * {@code false}
262 *
263 * @see java.util.function.Predicate
264 * @since 1.8
265 */
266 public static boolean isNull(Object obj) {
267 return obj == null;
268 }
269
270 /**
271 * Returns {@code true} if the provided reference is non-{@code null}
272 * otherwise returns {@code false}.
273 *
274 * @apiNote This method exists to be used as a
275 * {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)}
276 *
277 * @param obj a reference to be checked against {@code null}
278 * @return {@code true} if the provided reference is non-{@code null}
279 * otherwise {@code false}
280 *
281 * @see java.util.function.Predicate
282 * @since 1.8
283 */
284 public static boolean nonNull(Object obj) {
285 return obj != null;
286 }
287
288 /**
289 * Returns the first argument if it is non-{@code null} and
290 * otherwise returns the non-{@code null} second argument.
291 *
292 * @param obj an object
293 * @param defaultObj a non-{@code null} object to return if the first argument
294 * is {@code null}
295 * @param <T> the type of the reference
296 * @return the first argument if it is non-{@code null} and
297 * otherwise the second argument if it is non-{@code null}
298 * @throws NullPointerException if both {@code obj} is null and
299 * {@code defaultObj} is {@code null}
300 * @since 9
301 */
302 public static <T> T requireNonNullElse(T obj, T defaultObj) {
303 return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
304 }
305
306 /**
307 * Returns the first argument if it is non-{@code null} and otherwise
308 * returns the non-{@code null} value of {@code supplier.get()}.
309 *
310 * @param obj an object
311 * @param supplier of a non-{@code null} object to return if the first argument
312 * is {@code null}
313 * @param <T> the type of the first argument and return type
314 * @return the first argument if it is non-{@code null} and otherwise
315 * the value from {@code supplier.get()} if it is non-{@code null}
316 * @throws NullPointerException if both {@code obj} is null and
317 * either the {@code supplier} is {@code null} or
318 * the {@code supplier.get()} value is {@code null}
319 * @since 9
320 */
321 public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
322 return (obj != null) ? obj
323 : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
324 }
325
326 /**
327 * Checks that the specified object reference is not {@code null} and
328 * throws a customized {@link NullPointerException} if it is.
329 *
330 * <p>Unlike the method {@link #requireNonNull(Object, String)},
331 * this method allows creation of the message to be deferred until
332 * after the null check is made. While this may confer a
333 * performance advantage in the non-null case, when deciding to
334 * call this method care should be taken that the costs of
335 * creating the message supplier are less than the cost of just
336 * creating the string message directly.
337 *
338 * @param obj the object reference to check for nullity
339 * @param messageSupplier supplier of the detail message to be
340 * used in the event that a {@code NullPointerException} is thrown
341 * @param <T> the type of the reference
342 * @return {@code obj} if not {@code null}
343 * @throws NullPointerException if {@code obj} is {@code null}
344 * @since 1.8
345 */
346 public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
347 if (obj == null)
348 throw new NullPointerException(messageSupplier == null ?
349 null : messageSupplier.get());
350 return obj;
351 }
352
353 /**
354 * Checks if the {@code index} is within the bounds of the range from
355 * {@code 0} (inclusive) to {@code length} (exclusive).
356 *
357 * <p>The {@code index} is defined to be out of bounds if any of the
358 * following inequalities is true:
359 * <ul>
360 * <li>{@code index < 0}</li>
361 * <li>{@code index >= length}</li>
362 * <li>{@code length < 0}, which is implied from the former inequalities</li>
363 * </ul>
364 *
365 * @param index the index
366 * @param length the upper-bound (exclusive) of the range
367 * @return {@code index} if it is within bounds of the range
368 * @throws IndexOutOfBoundsException if the {@code index} is out of bounds
369 * @since 9
370 */
371 @ForceInline
372 public static
373 int checkIndex(int index, int length) {
374 return Preconditions.checkIndex(index, length, null);
375 }
376
377 /**
378 * Checks if the sub-range from {@code fromIndex} (inclusive) to
379 * {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
380 * (inclusive) to {@code length} (exclusive).
381 *
382 * <p>The sub-range is defined to be out of bounds if any of the following
383 * inequalities is true:
384 * <ul>
385 * <li>{@code fromIndex < 0}</li>
386 * <li>{@code fromIndex > toIndex}</li>
387 * <li>{@code toIndex > length}</li>
388 * <li>{@code length < 0}, which is implied from the former inequalities</li>
389 * </ul>
390 *
391 * @param fromIndex the lower-bound (inclusive) of the sub-range
392 * @param toIndex the upper-bound (exclusive) of the sub-range
393 * @param length the upper-bound (exclusive) the range
394 * @return {@code fromIndex} if the sub-range within bounds of the range
395 * @throws IndexOutOfBoundsException if the sub-range is out of bounds
396 * @since 9
397 */
398 public static
399 int checkFromToIndex(int fromIndex, int toIndex, int length) {
400 return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
401 }
402
403 /**
404 * Checks if the sub-range from {@code fromIndex} (inclusive) to
405 * {@code fromIndex + size} (exclusive) is within the bounds of range from
406 * {@code 0} (inclusive) to {@code length} (exclusive).
407 *
408 * <p>The sub-range is defined to be out of bounds if any of the following
409 * inequalities is true:
410 * <ul>
411 * <li>{@code fromIndex < 0}</li>
412 * <li>{@code size < 0}</li>
413 * <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
414 * <li>{@code length < 0}, which is implied from the former inequalities</li>
415 * </ul>
416 *
417 * @param fromIndex the lower-bound (inclusive) of the sub-interval
418 * @param size the size of the sub-range
419 * @param length the upper-bound (exclusive) of the range
420 * @return {@code fromIndex} if the sub-range within bounds of the range
421 * @throws IndexOutOfBoundsException if the sub-range is out of bounds
422 * @since 9
423 */
424 public static
425 int checkFromIndexSize(int fromIndex, int size, int length) {
426 return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
427 }
428
429 /**
430 * Return the size of the object in the heap.
431 *
432 * @param o an object
433 * @return the objects's size
434 * @since Valhalla
435 */
436 public static long getObjectSize(Object o) {
437 return Unsafe.getUnsafe().getObjectSize(o);
438 }
439 }