1 /*
2  * Copyright (c) 2009, 2020, 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 
30 import java.util.function.Supplier;
31 
32 /**
33  * This class consists of {@code static} utility methods for operating
34  * on objects, or checking certain conditions before operation.  These utilities
35  * include {@code null}-safe or {@code null}-tolerant methods for computing the
36  * hash code of an object, returning a string for an object, comparing two
37  * objects, and checking if indexes or sub-range values are out of bounds.
38  *
39  * @since 1.7
40  */
41 public final class Objects {
Objects()42     private Objects() {
43         throw new AssertionError("No java.util.Objects instances for you!");
44     }
45 
46     /**
47      * Returns {@code true} if the arguments are equal to each other
48      * and {@code false} otherwise.
49      * Consequently, if both arguments are {@code null}, {@code true}
50      * is returned.  Otherwise, if the first argument is not {@code
51      * null}, equality is determined by calling the {@link
52      * Object#equals equals} method of the first argument with the
53      * second argument of this method. Otherwise, {@code false} is
54      * returned.
55      *
56      * @param a an object
57      * @param b an object to be compared with {@code a} for equality
58      * @return {@code true} if the arguments are equal to each other
59      * and {@code false} otherwise
60      * @see Object#equals(Object)
61      */
equals(Object a, Object b)62     public static boolean equals(Object a, Object b) {
63         return (a == b) || (a != null && a.equals(b));
64     }
65 
66    /**
67     * Returns {@code true} if the arguments are deeply equal to each other
68     * and {@code false} otherwise.
69     *
70     * Two {@code null} values are deeply equal.  If both arguments are
71     * arrays, the algorithm in {@link Arrays#deepEquals(Object[],
72     * Object[]) Arrays.deepEquals} is used to determine equality.
73     * Otherwise, equality is determined by using the {@link
74     * Object#equals equals} method of the first argument.
75     *
76     * @param a an object
77     * @param b an object to be compared with {@code a} for deep equality
78     * @return {@code true} if the arguments are deeply equal to each other
79     * and {@code false} otherwise
80     * @see Arrays#deepEquals(Object[], Object[])
81     * @see Objects#equals(Object, Object)
82     */
deepEquals(Object a, Object b)83     public static boolean deepEquals(Object a, Object b) {
84         if (a == b)
85             return true;
86         else if (a == null || b == null)
87             return false;
88         else
89             return Arrays.deepEquals0(a, b);
90     }
91 
92     /**
93      * Returns the hash code of a non-{@code null} argument and 0 for
94      * a {@code null} argument.
95      *
96      * @param o an object
97      * @return the hash code of a non-{@code null} argument and 0 for
98      * a {@code null} argument
99      * @see Object#hashCode
100      */
hashCode(Object o)101     public static int hashCode(Object o) {
102         return o != null ? o.hashCode() : 0;
103     }
104 
105    /**
106     * Generates a hash code for a sequence of input values. The hash
107     * code is generated as if all the input values were placed into an
108     * array, and that array were hashed by calling {@link
109     * Arrays#hashCode(Object[])}.
110     *
111     * <p>This method is useful for implementing {@link
112     * Object#hashCode()} on objects containing multiple fields. For
113     * example, if an object that has three fields, {@code x}, {@code
114     * y}, and {@code z}, one could write:
115     *
116     * <blockquote><pre>
117     * &#064;Override public int hashCode() {
118     *     return Objects.hash(x, y, z);
119     * }
120     * </pre></blockquote>
121     *
122     * <b>Warning: When a single object reference is supplied, the returned
123     * value does not equal the hash code of that object reference.</b> This
124     * value can be computed by calling {@link #hashCode(Object)}.
125     *
126     * @param values the values to be hashed
127     * @return a hash value of the sequence of input values
128     * @see Arrays#hashCode(Object[])
129     * @see List#hashCode
130     */
hash(Object... values)131     public static int hash(Object... values) {
132         return Arrays.hashCode(values);
133     }
134 
135     /**
136      * Returns the result of calling {@code toString} for a non-{@code
137      * null} argument and {@code "null"} for a {@code null} argument.
138      *
139      * @param o an object
140      * @return the result of calling {@code toString} for a non-{@code
141      * null} argument and {@code "null"} for a {@code null} argument
142      * @see Object#toString
143      * @see String#valueOf(Object)
144      */
toString(Object o)145     public static String toString(Object o) {
146         return String.valueOf(o);
147     }
148 
149     /**
150      * Returns the result of calling {@code toString} on the first
151      * argument if the first argument is not {@code null} and returns
152      * the second argument otherwise.
153      *
154      * @param o an object
155      * @param nullDefault string to return if the first argument is
156      *        {@code null}
157      * @return the result of calling {@code toString} on the first
158      * argument if it is not {@code null} and the second argument
159      * otherwise.
160      * @see Objects#toString(Object)
161      */
toString(Object o, String nullDefault)162     public static String toString(Object o, String nullDefault) {
163         return (o != null) ? o.toString() : nullDefault;
164     }
165 
166     /**
167      * Returns 0 if the arguments are identical and {@code
168      * c.compare(a, b)} otherwise.
169      * Consequently, if both arguments are {@code null} 0
170      * is returned.
171      *
172      * <p>Note that if one of the arguments is {@code null}, a {@code
173      * NullPointerException} may or may not be thrown depending on
174      * what ordering policy, if any, the {@link Comparator Comparator}
175      * chooses to have for {@code null} values.
176      *
177      * @param <T> the type of the objects being compared
178      * @param a an object
179      * @param b an object to be compared with {@code a}
180      * @param c the {@code Comparator} to compare the first two arguments
181      * @return 0 if the arguments are identical and {@code
182      * c.compare(a, b)} otherwise.
183      * @see Comparable
184      * @see Comparator
185      */
compare(T a, T b, Comparator<? super T> c)186     public static <T> int compare(T a, T b, Comparator<? super T> c) {
187         return (a == b) ? 0 :  c.compare(a, b);
188     }
189 
190     /**
191      * Checks that the specified object reference is not {@code null}. This
192      * method is designed primarily for doing parameter validation in methods
193      * and constructors, as demonstrated below:
194      * <blockquote><pre>
195      * public Foo(Bar bar) {
196      *     this.bar = Objects.requireNonNull(bar);
197      * }
198      * </pre></blockquote>
199      *
200      * @param obj the object reference to check for nullity
201      * @param <T> the type of the reference
202      * @return {@code obj} if not {@code null}
203      * @throws NullPointerException if {@code obj} is {@code null}
204      */
requireNonNull(T obj)205     public static <T> T requireNonNull(T obj) {
206         if (obj == null)
207             throw new NullPointerException();
208         return obj;
209     }
210 
211     /**
212      * Checks that the specified object reference is not {@code null} and
213      * throws a customized {@link NullPointerException} if it is. This method
214      * is designed primarily for doing parameter validation in methods and
215      * constructors with multiple parameters, as demonstrated below:
216      * <blockquote><pre>
217      * public Foo(Bar bar, Baz baz) {
218      *     this.bar = Objects.requireNonNull(bar, "bar must not be null");
219      *     this.baz = Objects.requireNonNull(baz, "baz must not be null");
220      * }
221      * </pre></blockquote>
222      *
223      * @param obj     the object reference to check for nullity
224      * @param message detail message to be used in the event that a {@code
225      *                NullPointerException} is thrown
226      * @param <T> the type of the reference
227      * @return {@code obj} if not {@code null}
228      * @throws NullPointerException if {@code obj} is {@code null}
229      */
requireNonNull(T obj, String message)230     public static <T> T requireNonNull(T obj, String message) {
231         if (obj == null)
232             throw new NullPointerException(message);
233         return obj;
234     }
235 
236     /**
237      * Returns {@code true} if the provided reference is {@code null} otherwise
238      * returns {@code false}.
239      *
240      * @apiNote This method exists to be used as a
241      * {@link java.util.function.Predicate}, {@code filter(Objects::isNull)}
242      *
243      * @param obj a reference to be checked against {@code null}
244      * @return {@code true} if the provided reference is {@code null} otherwise
245      * {@code false}
246      *
247      * @see java.util.function.Predicate
248      * @since 1.8
249      */
isNull(Object obj)250     public static boolean isNull(Object obj) {
251         return obj == null;
252     }
253 
254     /**
255      * Returns {@code true} if the provided reference is non-{@code null}
256      * otherwise returns {@code false}.
257      *
258      * @apiNote This method exists to be used as a
259      * {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)}
260      *
261      * @param obj a reference to be checked against {@code null}
262      * @return {@code true} if the provided reference is non-{@code null}
263      * otherwise {@code false}
264      *
265      * @see java.util.function.Predicate
266      * @since 1.8
267      */
nonNull(Object obj)268     public static boolean nonNull(Object obj) {
269         return obj != null;
270     }
271 
272     /**
273      * Returns the first argument if it is non-{@code null} and
274      * otherwise returns the non-{@code null} second argument.
275      *
276      * @param obj an object
277      * @param defaultObj a non-{@code null} object to return if the first argument
278      *                   is {@code null}
279      * @param <T> the type of the reference
280      * @return the first argument if it is non-{@code null} and
281      *        otherwise the second argument if it is non-{@code null}
282      * @throws NullPointerException if both {@code obj} is null and
283      *        {@code defaultObj} is {@code null}
284      * @since 9
285      */
requireNonNullElse(T obj, T defaultObj)286     public static <T> T requireNonNullElse(T obj, T defaultObj) {
287         return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
288     }
289 
290     /**
291      * Returns the first argument if it is non-{@code null} and otherwise
292      * returns the non-{@code null} value of {@code supplier.get()}.
293      *
294      * @param obj an object
295      * @param supplier of a non-{@code null} object to return if the first argument
296      *                 is {@code null}
297      * @param <T> the type of the first argument and return type
298      * @return the first argument if it is non-{@code null} and otherwise
299      *         the value from {@code supplier.get()} if it is non-{@code null}
300      * @throws NullPointerException if both {@code obj} is null and
301      *        either the {@code supplier} is {@code null} or
302      *        the {@code supplier.get()} value is {@code null}
303      * @since 9
304      */
requireNonNullElseGet(T obj, Supplier<? extends T> supplier)305     public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
306         return (obj != null) ? obj
307                 : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
308     }
309 
310     /**
311      * Checks that the specified object reference is not {@code null} and
312      * throws a customized {@link NullPointerException} if it is.
313      *
314      * <p>Unlike the method {@link #requireNonNull(Object, String)},
315      * this method allows creation of the message to be deferred until
316      * after the null check is made. While this may confer a
317      * performance advantage in the non-null case, when deciding to
318      * call this method care should be taken that the costs of
319      * creating the message supplier are less than the cost of just
320      * creating the string message directly.
321      *
322      * @param obj     the object reference to check for nullity
323      * @param messageSupplier supplier of the detail message to be
324      * used in the event that a {@code NullPointerException} is thrown
325      * @param <T> the type of the reference
326      * @return {@code obj} if not {@code null}
327      * @throws NullPointerException if {@code obj} is {@code null}
328      * @since 1.8
329      */
requireNonNull(T obj, Supplier<String> messageSupplier)330     public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {
331         if (obj == null)
332             throw new NullPointerException(messageSupplier == null ?
333                                            null : messageSupplier.get());
334         return obj;
335     }
336 
337     /**
338      * Checks if the {@code index} is within the bounds of the range from
339      * {@code 0} (inclusive) to {@code length} (exclusive).
340      *
341      * <p>The {@code index} is defined to be out of bounds if any of the
342      * following inequalities is true:
343      * <ul>
344      *  <li>{@code index < 0}</li>
345      *  <li>{@code index >= length}</li>
346      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
347      * </ul>
348      *
349      * @param index the index
350      * @param length the upper-bound (exclusive) of the range
351      * @return {@code index} if it is within bounds of the range
352      * @throws IndexOutOfBoundsException if the {@code index} is out of bounds
353      * @since 9
354      */
355     // Android-removed: @ForceInline is an unsupported attribute.
356     //@ForceInline
357     public static
checkIndex(int index, int length)358     int checkIndex(int index, int length) {
359         return Preconditions.checkIndex(index, length, null);
360     }
361 
362     /**
363      * Checks if the sub-range from {@code fromIndex} (inclusive) to
364      * {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
365      * (inclusive) to {@code length} (exclusive).
366      *
367      * <p>The sub-range is defined to be out of bounds if any of the following
368      * inequalities is true:
369      * <ul>
370      *  <li>{@code fromIndex < 0}</li>
371      *  <li>{@code fromIndex > toIndex}</li>
372      *  <li>{@code toIndex > length}</li>
373      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
374      * </ul>
375      *
376      * @param fromIndex the lower-bound (inclusive) of the sub-range
377      * @param toIndex the upper-bound (exclusive) of the sub-range
378      * @param length the upper-bound (exclusive) the range
379      * @return {@code fromIndex} if the sub-range within bounds of the range
380      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
381      * @since 9
382      */
383     public static
checkFromToIndex(int fromIndex, int toIndex, int length)384     int checkFromToIndex(int fromIndex, int toIndex, int length) {
385         return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
386     }
387 
388     /**
389      * Checks if the sub-range from {@code fromIndex} (inclusive) to
390      * {@code fromIndex + size} (exclusive) is within the bounds of range from
391      * {@code 0} (inclusive) to {@code length} (exclusive).
392      *
393      * <p>The sub-range is defined to be out of bounds if any of the following
394      * inequalities is true:
395      * <ul>
396      *  <li>{@code fromIndex < 0}</li>
397      *  <li>{@code size < 0}</li>
398      *  <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
399      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
400      * </ul>
401      *
402      * @param fromIndex the lower-bound (inclusive) of the sub-interval
403      * @param size the size of the sub-range
404      * @param length the upper-bound (exclusive) of the range
405      * @return {@code fromIndex} if the sub-range within bounds of the range
406      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
407      * @since 9
408      */
409     public static
checkFromIndexSize(int fromIndex, int size, int length)410     int checkFromIndexSize(int fromIndex, int size, int length) {
411         return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
412     }
413 
414     /**
415      * Checks if the {@code index} is within the bounds of the range from
416      * {@code 0} (inclusive) to {@code length} (exclusive).
417      *
418      * <p>The {@code index} is defined to be out of bounds if any of the
419      * following inequalities is true:
420      * <ul>
421      *  <li>{@code index < 0}</li>
422      *  <li>{@code index >= length}</li>
423      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
424      * </ul>
425      *
426      * @param index the index
427      * @param length the upper-bound (exclusive) of the range
428      * @return {@code index} if it is within bounds of the range
429      * @throws IndexOutOfBoundsException if the {@code index} is out of bounds
430      * @since 16
431      */
432     // Android-removed: @ForceInline is an unsupported attribute.
433     //@ForceInline
434     public static
checkIndex(long index, long length)435     long checkIndex(long index, long length) {
436         return Preconditions.checkIndex(index, length, null);
437     }
438 
439     /**
440      * Checks if the sub-range from {@code fromIndex} (inclusive) to
441      * {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
442      * (inclusive) to {@code length} (exclusive).
443      *
444      * <p>The sub-range is defined to be out of bounds if any of the following
445      * inequalities is true:
446      * <ul>
447      *  <li>{@code fromIndex < 0}</li>
448      *  <li>{@code fromIndex > toIndex}</li>
449      *  <li>{@code toIndex > length}</li>
450      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
451      * </ul>
452      *
453      * @param fromIndex the lower-bound (inclusive) of the sub-range
454      * @param toIndex the upper-bound (exclusive) of the sub-range
455      * @param length the upper-bound (exclusive) the range
456      * @return {@code fromIndex} if the sub-range within bounds of the range
457      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
458      * @since 16
459      */
460     public static
checkFromToIndex(long fromIndex, long toIndex, long length)461     long checkFromToIndex(long fromIndex, long toIndex, long length) {
462         return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
463     }
464 
465     /**
466      * Checks if the sub-range from {@code fromIndex} (inclusive) to
467      * {@code fromIndex + size} (exclusive) is within the bounds of range from
468      * {@code 0} (inclusive) to {@code length} (exclusive).
469      *
470      * <p>The sub-range is defined to be out of bounds if any of the following
471      * inequalities is true:
472      * <ul>
473      *  <li>{@code fromIndex < 0}</li>
474      *  <li>{@code size < 0}</li>
475      *  <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
476      *  <li>{@code length < 0}, which is implied from the former inequalities</li>
477      * </ul>
478      *
479      * @param fromIndex the lower-bound (inclusive) of the sub-interval
480      * @param size the size of the sub-range
481      * @param length the upper-bound (exclusive) of the range
482      * @return {@code fromIndex} if the sub-range within bounds of the range
483      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
484      * @since 16
485      */
486     public static
checkFromIndexSize(long fromIndex, long size, long length)487     long checkFromIndexSize(long fromIndex, long size, long length) {
488         return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
489     }
490 }
491