/*

 * Copyright 2009 Sun Microsystems, Inc.  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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.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 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 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;

    }

    /**

     * 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 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.nonNull(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 nonNull(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.nonNull(bar, "bar must not be null");

     *     this.baz = Objects.nonNull(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 nonNull(T obj, String message) {

        if (obj == null)

            throw new NullPointerException(message);

        return obj;

    }

}