/*

 * Copyright (c) 2009, 2013, 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;

import java.util.function.Supplier;

/**

 * 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;

    }

    /**

     * Returns {@code true} if the provided reference is {@code null} otherwise

     * returns {@code false}.

     *

     * @apiNote This method exists to be used as a

     * {@link java.util.function.Predicate}, {@code filter(Objects::isNull)}

     *

     * @param obj a reference to be checked against {@code null}

     * @return {@code true} if the provided reference is {@code null} otherwise

     * {@code false}

     *

     * @see java.util.function.Predicate

     * @since 1.8

     */

    public static boolean isNull(Object obj) {

        return obj == null;

    }

    /**

     * Returns {@code true} if the provided reference is non-{@code null}

     * otherwise returns {@code false}.

     *

     * @apiNote This method exists to be used as a

     * {@link java.util.function.Predicate}, {@code filter(Objects::nonNull)}

     *

     * @param obj a reference to be checked against {@code null}

     * @return {@code true} if the provided reference is non-{@code null}

     * otherwise {@code false}

     *

     * @see java.util.function.Predicate

     * @since 1.8

     */

    public static boolean nonNull(Object obj) {

        return obj != null;

    }

    /**

     * Checks that the specified object reference is not {@code null} and

     * throws a customized {@link NullPointerException} if it is.

     *

     * <p>Unlike the method {@link #requireNonNull(Object, String)},

     * this method allows creation of the message to be deferred until

     * after the null check is made. While this may confer a

     * performance advantage in the non-null case, when deciding to

     * call this method care should be taken that the costs of

     * creating the message supplier are less than the cost of just

     * creating the string message directly.

     *

     * @param obj     the object reference to check for nullity

     * @param messageSupplier supplier of the 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}

     * @since 1.8

     */

    public static <T> T requireNonNull(T obj, Supplier<String> messageSupplier) {

        if (obj == null)

            throw new NullPointerException(messageSupplier.get());

        return obj;

    }

}