| /* |
| * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved. |
| * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
| * |
| * This code is free software; you can redistribute it and/or modify it |
| * under the terms of the GNU General Public License version 2 only, as |
| * published by the Free Software Foundation. Oracle designates this |
| * particular file as subject to the "Classpath" exception as provided |
| * by Oracle in the LICENSE file that accompanied this code. |
| * |
| * This code is distributed in the hope that it will be useful, but WITHOUT |
| * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
| * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
| * version 2 for more details (a copy is included in the LICENSE file that |
| * accompanied this code). |
| * |
| * You should have received a copy of the GNU General Public License version |
| * 2 along with this work; if not, write to the Free Software Foundation, |
| * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
| * |
| * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
| * or visit www.oracle.com if you need additional information or have any |
| * questions. |
| */ |
| |
| package java.util; |
| |
| /** |
| * This class consists of {@code static} utility methods for operating |
| * on objects. These utilities include {@code null}-safe or {@code |
| * null}-tolerant methods for computing the hash code of an object, |
| * returning a string for an object, and comparing two objects. |
| * |
| * @since 1.7 |
| */ |
| public final class Objects { |
| private Objects() { |
| throw new AssertionError("No java.util.Objects instances for you!"); |
| } |
| |
| /** |
| * Returns {@code true} if the arguments are equal to each other |
| * and {@code false} otherwise. |
| * Consequently, if both arguments are {@code null}, {@code true} |
| * is returned and if exactly one argument is {@code null}, {@code |
| * false} is returned. Otherwise, equality is determined by using |
| * the {@link Object#equals equals} method of the first |
| * argument. |
| * |
| * @param a an object |
| * @param b an object to be compared with {@code a} for equality |
| * @return {@code true} if the arguments are equal to each other |
| * and {@code false} otherwise |
| * @see Object#equals(Object) |
| */ |
| public static boolean equals(Object a, Object b) { |
| return (a == b) || (a != null && a.equals(b)); |
| } |
| |
| /** |
| * Returns {@code true} if the arguments are deeply equal to each other |
| * and {@code false} otherwise. |
| * |
| * Two {@code null} values are deeply equal. If both arguments are |
| * arrays, the algorithm in {@link Arrays#deepEquals(Object[], |
| * Object[]) Arrays.deepEquals} is used to determine equality. |
| * Otherwise, equality is determined by using the {@link |
| * Object#equals equals} method of the first argument. |
| * |
| * @param a an object |
| * @param b an object to be compared with {@code a} for deep equality |
| * @return {@code true} if the arguments are deeply equal to each other |
| * and {@code false} otherwise |
| * @see Arrays#deepEquals(Object[], Object[]) |
| * @see Objects#equals(Object, Object) |
| */ |
| public static boolean deepEquals(Object a, Object b) { |
| if (a == b) |
| return true; |
| else if (a == null || b == null) |
| return false; |
| else |
| return Arrays.deepEquals0(a, b); |
| } |
| |
| /** |
| * Returns the hash code of a non-{@code null} argument and 0 for |
| * a {@code null} argument. |
| * |
| * @param o an object |
| * @return the hash code of a non-{@code null} argument and 0 for |
| * a {@code null} argument |
| * @see Object#hashCode |
| */ |
| public static int hashCode(Object o) { |
| return o != null ? o.hashCode() : 0; |
| } |
| |
| /** |
| * Generates a hash code for a sequence of input values. The hash |
| * code is generated as if all the input values were placed into an |
| * array, and that array were hashed by calling {@link |
| * Arrays#hashCode(Object[])}. |
| * |
| * <p>This method is useful for implementing {@link |
| * Object#hashCode()} on objects containing multiple fields. For |
| * example, if an object that has three fields, {@code x}, {@code |
| * y}, and {@code z}, one could write: |
| * |
| * <blockquote><pre> |
| * @Override public int hashCode() { |
| * return Objects.hash(x, y, z); |
| * } |
| * </pre></blockquote> |
| * |
| * <b>Warning: When a single object reference is supplied, the returned |
| * value does not equal the hash code of that object reference.</b> This |
| * value can be computed by calling {@link #hashCode(Object)}. |
| * |
| * @param values the values to be hashed |
| * @return a hash value of the sequence of input values |
| * @see Arrays#hashCode(Object[]) |
| * @see List#hashCode |
| */ |
| public static int hash(Object... values) { |
| return Arrays.hashCode(values); |
| } |
| |
| /** |
| * Returns the result of calling {@code toString} for a non-{@code |
| * null} argument and {@code "null"} for a {@code null} argument. |
| * |
| * @param o an object |
| * @return the result of calling {@code toString} for a non-{@code |
| * null} argument and {@code "null"} for a {@code null} argument |
| * @see Object#toString |
| * @see String#valueOf(Object) |
| */ |
| public static String toString(Object o) { |
| return String.valueOf(o); |
| } |
| |
| /** |
| * Returns the result of calling {@code toString} on the first |
| * argument if the first argument is not {@code null} and returns |
| * the second argument otherwise. |
| * |
| * @param o an object |
| * @param nullDefault string to return if the first argument is |
| * {@code null} |
| * @return the result of calling {@code toString} on the first |
| * argument if it is not {@code null} and the second argument |
| * otherwise. |
| * @see Objects#toString(Object) |
| */ |
| public static String toString(Object o, String nullDefault) { |
| return (o != null) ? o.toString() : nullDefault; |
| } |
| |
| /** |
| * Returns 0 if the arguments are identical and {@code |
| * c.compare(a, b)} otherwise. |
| * Consequently, if both arguments are {@code null} 0 |
| * is returned. |
| * |
| * <p>Note that if one of the arguments is {@code null}, a {@code |
| * NullPointerException} may or may not be thrown depending on |
| * what ordering policy, if any, the {@link Comparator Comparator} |
| * chooses to have for {@code null} values. |
| * |
| * @param <T> the type of the objects being compared |
| * @param a an object |
| * @param b an object to be compared with {@code a} |
| * @param c the {@code Comparator} to compare the first two arguments |
| * @return 0 if the arguments are identical and {@code |
| * c.compare(a, b)} otherwise. |
| * @see Comparable |
| * @see Comparator |
| */ |
| public static <T> int compare(T a, T b, Comparator<? super T> c) { |
| return (a == b) ? 0 : c.compare(a, b); |
| } |
| |
| /** |
| * Checks that the specified object reference is not {@code null}. This |
| * method is designed primarily for doing parameter validation in methods |
| * and constructors, as demonstrated below: |
| * <blockquote><pre> |
| * public Foo(Bar bar) { |
| * this.bar = Objects.requireNonNull(bar); |
| * } |
| * </pre></blockquote> |
| * |
| * @param obj the object reference to check for nullity |
| * @param <T> the type of the reference |
| * @return {@code obj} if not {@code null} |
| * @throws NullPointerException if {@code obj} is {@code null} |
| */ |
| public static <T> T requireNonNull(T obj) { |
| if (obj == null) |
| throw new NullPointerException(); |
| return obj; |
| } |
| |
| /** |
| * Checks that the specified object reference is not {@code null} and |
| * throws a customized {@link NullPointerException} if it is. This method |
| * is designed primarily for doing parameter validation in methods and |
| * constructors with multiple parameters, as demonstrated below: |
| * <blockquote><pre> |
| * public Foo(Bar bar, Baz baz) { |
| * this.bar = Objects.requireNonNull(bar, "bar must not be null"); |
| * this.baz = Objects.requireNonNull(baz, "baz must not be null"); |
| * } |
| * </pre></blockquote> |
| * |
| * @param obj the object reference to check for nullity |
| * @param message detail message to be used in the event that a {@code |
| * NullPointerException} is thrown |
| * @param <T> the type of the reference |
| * @return {@code obj} if not {@code null} |
| * @throws NullPointerException if {@code obj} is {@code null} |
| */ |
| public static <T> T requireNonNull(T obj, String message) { |
| if (obj == null) |
| throw new NullPointerException(message); |
| return obj; |
| } |
| } |
