jaroslav@682: /*
jaroslav@682:  * Copyright (c) 2009, 2011, Oracle and/or its affiliates. All rights reserved.
jaroslav@682:  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
jaroslav@682:  *
jaroslav@682:  * This code is free software; you can redistribute it and/or modify it
jaroslav@682:  * under the terms of the GNU General Public License version 2 only, as
jaroslav@682:  * published by the Free Software Foundation.  Oracle designates this
jaroslav@682:  * particular file as subject to the "Classpath" exception as provided
jaroslav@682:  * by Oracle in the LICENSE file that accompanied this code.
jaroslav@682:  *
jaroslav@682:  * This code is distributed in the hope that it will be useful, but WITHOUT
jaroslav@682:  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
jaroslav@682:  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
jaroslav@682:  * version 2 for more details (a copy is included in the LICENSE file that
jaroslav@682:  * accompanied this code).
jaroslav@682:  *
jaroslav@682:  * You should have received a copy of the GNU General Public License version
jaroslav@682:  * 2 along with this work; if not, write to the Free Software Foundation,
jaroslav@682:  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
jaroslav@682:  *
jaroslav@682:  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
jaroslav@682:  * or visit www.oracle.com if you need additional information or have any
jaroslav@682:  * questions.
jaroslav@682:  */
jaroslav@682: 
jaroslav@682: package java.util;
jaroslav@682: 
jaroslav@682: /**
jaroslav@682:  * This class consists of {@code static} utility methods for operating
jaroslav@682:  * on objects.  These utilities include {@code null}-safe or {@code
jaroslav@682:  * null}-tolerant methods for computing the hash code of an object,
jaroslav@682:  * returning a string for an object, and comparing two objects.
jaroslav@682:  *
jaroslav@682:  * @since 1.7
jaroslav@682:  */
jaroslav@682: public final class Objects {
jaroslav@682:     private Objects() {
jaroslav@682:         throw new AssertionError("No java.util.Objects instances for you!");
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Returns {@code true} if the arguments are equal to each other
jaroslav@682:      * and {@code false} otherwise.
jaroslav@682:      * Consequently, if both arguments are {@code null}, {@code true}
jaroslav@682:      * is returned and if exactly one argument is {@code null}, {@code
jaroslav@682:      * false} is returned.  Otherwise, equality is determined by using
jaroslav@682:      * the {@link Object#equals equals} method of the first
jaroslav@682:      * argument.
jaroslav@682:      *
jaroslav@682:      * @param a an object
jaroslav@682:      * @param b an object to be compared with {@code a} for equality
jaroslav@682:      * @return {@code true} if the arguments are equal to each other
jaroslav@682:      * and {@code false} otherwise
jaroslav@682:      * @see Object#equals(Object)
jaroslav@682:      */
jaroslav@682:     public static boolean equals(Object a, Object b) {
jaroslav@682:         return (a == b) || (a != null && a.equals(b));
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:    /**
jaroslav@682:     * Returns {@code true} if the arguments are deeply equal to each other
jaroslav@682:     * and {@code false} otherwise.
jaroslav@682:     *
jaroslav@682:     * Two {@code null} values are deeply equal.  If both arguments are
jaroslav@682:     * arrays, the algorithm in {@link Arrays#deepEquals(Object[],
jaroslav@682:     * Object[]) Arrays.deepEquals} is used to determine equality.
jaroslav@682:     * Otherwise, equality is determined by using the {@link
jaroslav@682:     * Object#equals equals} method of the first argument.
jaroslav@682:     *
jaroslav@682:     * @param a an object
jaroslav@682:     * @param b an object to be compared with {@code a} for deep equality
jaroslav@682:     * @return {@code true} if the arguments are deeply equal to each other
jaroslav@682:     * and {@code false} otherwise
jaroslav@682:     * @see Arrays#deepEquals(Object[], Object[])
jaroslav@682:     * @see Objects#equals(Object, Object)
jaroslav@682:     */
jaroslav@682:     public static boolean deepEquals(Object a, Object b) {
jaroslav@682:         if (a == b)
jaroslav@682:             return true;
jaroslav@682:         else if (a == null || b == null)
jaroslav@682:             return false;
jaroslav@682:         else
jaroslav@682:             return Arrays.deepEquals0(a, b);
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Returns the hash code of a non-{@code null} argument and 0 for
jaroslav@682:      * a {@code null} argument.
jaroslav@682:      *
jaroslav@682:      * @param o an object
jaroslav@682:      * @return the hash code of a non-{@code null} argument and 0 for
jaroslav@682:      * a {@code null} argument
jaroslav@682:      * @see Object#hashCode
jaroslav@682:      */
jaroslav@682:     public static int hashCode(Object o) {
jaroslav@682:         return o != null ? o.hashCode() : 0;
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:    /**
jaroslav@682:     * Generates a hash code for a sequence of input values. The hash
jaroslav@682:     * code is generated as if all the input values were placed into an
jaroslav@682:     * array, and that array were hashed by calling {@link
jaroslav@682:     * Arrays#hashCode(Object[])}.
jaroslav@682:     *
jaroslav@682:     * <p>This method is useful for implementing {@link
jaroslav@682:     * Object#hashCode()} on objects containing multiple fields. For
jaroslav@682:     * example, if an object that has three fields, {@code x}, {@code
jaroslav@682:     * y}, and {@code z}, one could write:
jaroslav@682:     *
jaroslav@682:     * <blockquote><pre>
jaroslav@682:     * &#064;Override public int hashCode() {
jaroslav@682:     *     return Objects.hash(x, y, z);
jaroslav@682:     * }
jaroslav@682:     * </pre></blockquote>
jaroslav@682:     *
jaroslav@682:     * <b>Warning: When a single object reference is supplied, the returned
jaroslav@682:     * value does not equal the hash code of that object reference.</b> This
jaroslav@682:     * value can be computed by calling {@link #hashCode(Object)}.
jaroslav@682:     *
jaroslav@682:     * @param values the values to be hashed
jaroslav@682:     * @return a hash value of the sequence of input values
jaroslav@682:     * @see Arrays#hashCode(Object[])
jaroslav@682:     * @see List#hashCode
jaroslav@682:     */
jaroslav@682:     public static int hash(Object... values) {
jaroslav@682:         return Arrays.hashCode(values);
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Returns the result of calling {@code toString} for a non-{@code
jaroslav@682:      * null} argument and {@code "null"} for a {@code null} argument.
jaroslav@682:      *
jaroslav@682:      * @param o an object
jaroslav@682:      * @return the result of calling {@code toString} for a non-{@code
jaroslav@682:      * null} argument and {@code "null"} for a {@code null} argument
jaroslav@682:      * @see Object#toString
jaroslav@682:      * @see String#valueOf(Object)
jaroslav@682:      */
jaroslav@682:     public static String toString(Object o) {
jaroslav@682:         return String.valueOf(o);
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Returns the result of calling {@code toString} on the first
jaroslav@682:      * argument if the first argument is not {@code null} and returns
jaroslav@682:      * the second argument otherwise.
jaroslav@682:      *
jaroslav@682:      * @param o an object
jaroslav@682:      * @param nullDefault string to return if the first argument is
jaroslav@682:      *        {@code null}
jaroslav@682:      * @return the result of calling {@code toString} on the first
jaroslav@682:      * argument if it is not {@code null} and the second argument
jaroslav@682:      * otherwise.
jaroslav@682:      * @see Objects#toString(Object)
jaroslav@682:      */
jaroslav@682:     public static String toString(Object o, String nullDefault) {
jaroslav@682:         return (o != null) ? o.toString() : nullDefault;
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Returns 0 if the arguments are identical and {@code
jaroslav@682:      * c.compare(a, b)} otherwise.
jaroslav@682:      * Consequently, if both arguments are {@code null} 0
jaroslav@682:      * is returned.
jaroslav@682:      *
jaroslav@682:      * <p>Note that if one of the arguments is {@code null}, a {@code
jaroslav@682:      * NullPointerException} may or may not be thrown depending on
jaroslav@682:      * what ordering policy, if any, the {@link Comparator Comparator}
jaroslav@682:      * chooses to have for {@code null} values.
jaroslav@682:      *
jaroslav@682:      * @param <T> the type of the objects being compared
jaroslav@682:      * @param a an object
jaroslav@682:      * @param b an object to be compared with {@code a}
jaroslav@682:      * @param c the {@code Comparator} to compare the first two arguments
jaroslav@682:      * @return 0 if the arguments are identical and {@code
jaroslav@682:      * c.compare(a, b)} otherwise.
jaroslav@682:      * @see Comparable
jaroslav@682:      * @see Comparator
jaroslav@682:      */
jaroslav@682:     public static <T> int compare(T a, T b, Comparator<? super T> c) {
jaroslav@682:         return (a == b) ? 0 :  c.compare(a, b);
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Checks that the specified object reference is not {@code null}. This
jaroslav@682:      * method is designed primarily for doing parameter validation in methods
jaroslav@682:      * and constructors, as demonstrated below:
jaroslav@682:      * <blockquote><pre>
jaroslav@682:      * public Foo(Bar bar) {
jaroslav@682:      *     this.bar = Objects.requireNonNull(bar);
jaroslav@682:      * }
jaroslav@682:      * </pre></blockquote>
jaroslav@682:      *
jaroslav@682:      * @param obj the object reference to check for nullity
jaroslav@682:      * @param <T> the type of the reference
jaroslav@682:      * @return {@code obj} if not {@code null}
jaroslav@682:      * @throws NullPointerException if {@code obj} is {@code null}
jaroslav@682:      */
jaroslav@682:     public static <T> T requireNonNull(T obj) {
jaroslav@682:         if (obj == null)
jaroslav@682:             throw new NullPointerException();
jaroslav@682:         return obj;
jaroslav@682:     }
jaroslav@682: 
jaroslav@682:     /**
jaroslav@682:      * Checks that the specified object reference is not {@code null} and
jaroslav@682:      * throws a customized {@link NullPointerException} if it is. This method
jaroslav@682:      * is designed primarily for doing parameter validation in methods and
jaroslav@682:      * constructors with multiple parameters, as demonstrated below:
jaroslav@682:      * <blockquote><pre>
jaroslav@682:      * public Foo(Bar bar, Baz baz) {
jaroslav@682:      *     this.bar = Objects.requireNonNull(bar, "bar must not be null");
jaroslav@682:      *     this.baz = Objects.requireNonNull(baz, "baz must not be null");
jaroslav@682:      * }
jaroslav@682:      * </pre></blockquote>
jaroslav@682:      *
jaroslav@682:      * @param obj     the object reference to check for nullity
jaroslav@682:      * @param message detail message to be used in the event that a {@code
jaroslav@682:      *                NullPointerException} is thrown
jaroslav@682:      * @param <T> the type of the reference
jaroslav@682:      * @return {@code obj} if not {@code null}
jaroslav@682:      * @throws NullPointerException if {@code obj} is {@code null}
jaroslav@682:      */
jaroslav@682:     public static <T> T requireNonNull(T obj, String message) {
jaroslav@682:         if (obj == null)
jaroslav@682:             throw new NullPointerException(message);
jaroslav@682:         return obj;
jaroslav@682:     }
jaroslav@682: }