/* * Copyright (c) 2009, 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[])}. * *

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: * * 

    * @Override public int hashCode() {
    *     return Objects.hash(x, y, z);
    * }
    *
* * Warning: When a single object reference is supplied, the returned * value does not equal the hash code of that object reference. 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. * *

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 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 int compare(T a, T b, Comparator 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: * 

     * public Foo(Bar bar) {
     *     this.bar = Objects.requireNonNull(bar);
     * }
     *
* * @param obj the object reference to check for nullity * @param the type of the reference * @return {@code obj} if not {@code null} * @throws NullPointerException if {@code obj} is {@code null} */ public static 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: * 
     * 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");
     * }
     *
* * @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 the type of the reference * @return {@code obj} if not {@code null} * @throws NullPointerException if {@code obj} is {@code null} */ public static T requireNonNull(T obj, String message) { if (obj == null) throw new NullPointerException(message); return obj; } }