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   * 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
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   */
  
  package java.util;
  
  import jdk.internal.util.Preconditions;
  
  import java.util.function.Supplier;
  
  /**
   * This class consists of {@code static} utility methods for operating
   * on objects, or checking certain conditions before operation.  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, comparing two
   * objects, and checking if indexes or sub-range values are out-of-bounds.
   *
   * @apiNote
   * Static methods such as {@link Objects#checkIndex},
   * {@link Objects#checkFromToIndex}, and {@link Objects#checkFromIndexSize} are
   * provided for the convenience of checking if values corresponding to indexes
   * and sub-ranges are out-of-bounds.
   * Variations of these static methods support customization of the runtime
   * exception, and corresponding exception detail message, that is thrown when
   * values are out-of-bounds.  Such methods accept a functional interface
   * argument, instances of {@code BiFunction}, that maps out-of-bound values to a
   * runtime exception.  Care should be taken when using such methods in
   * combination with an argument that is a lambda expression, method reference or
   * class that capture values.  In such cases the cost of capture, related to
   * functional interface allocation, may exceed the cost of checking bounds.
   *
   * @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>
      * &#064;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;
      }
  
      /**
       * Returns the first argument if it is non-{@code null} and
       * otherwise returns the non-{@code null} second argument.
       *
       * @param obj an object
       * @param defaultObj a non-{@code null} object to return if the first argument
       *                   is {@code null}
       * @param <T> the type of the reference
       * @return the first argument if it is non-{@code null} and
       *        otherwise the second argument if it is non-{@code null}
       * @throws NullPointerException if both {@code obj} is null and
       *        {@code defaultObj} is {@code null}
       * @since 9
       */
      public static <T> T requireNonNullElse(T obj, T defaultObj) {
          return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
      }
  
      /**
       * Returns the first argument if it is non-{@code null} and otherwise
       * returns the non-{@code null} value of {@code supplier.get()}.
       *
       * @param obj an object
       * @param supplier of a non-{@code null} object to return if the first argument
       *                 is {@code null}
       * @param <T> the type of the first argument and return type
       * @return the first argument if it is non-{@code null} and otherwise
       *         the value from {@code supplier.get()} if it is non-{@code null}
       * @throws NullPointerException if both {@code obj} is null and
       *        either the {@code supplier} is {@code null} or
       *        the {@code supplier.get()} value is {@code null}
       * @since 9
       */
      public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier) {
          return (obj != null) ? obj
                  : requireNonNull(requireNonNull(supplier, "supplier").get(), "supplier.get()");
      }
  
      /**
       * 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 == null ?
                                             null : messageSupplier.get());
          return obj;
      }
  
      /**
       * Checks if the {@code index} is within the bounds of the range from
       * {@code 0} (inclusive) to {@code length} (exclusive).
       *
       * <p>The {@code index} is defined to be out-of-bounds if any of the
       * following inequalities is true:
       * <ul>
       *  <li>{@code index < 0}</li>
       *  <li>{@code index >= length}</li>
       *  <li>{@code length < 0}, which is implied from the former inequalities</li>
       * </ul>
       *
       * @param index the index
       * @param length the upper-bound (exclusive) of the range
       * @return {@code index} if it is within bounds of the range
       * @throws IndexOutOfBoundsException if the {@code index} is out-of-bounds
       * @since 9
       */
      // Android-removed: @ForceInline is an unsupported attribute.
      //@ForceInline
      public static
      int checkIndex(int index, int length) {
          return Preconditions.checkIndex(index, length, null);
      }
  
      /**
       * Checks if the sub-range from {@code fromIndex} (inclusive) to
       * {@code toIndex} (exclusive) is within the bounds of range from {@code 0}
       * (inclusive) to {@code length} (exclusive).
       *
       * <p>The sub-range is defined to be out-of-bounds if any of the following
       * inequalities is true:
       * <ul>
       *  <li>{@code fromIndex < 0}</li>
       *  <li>{@code fromIndex > toIndex}</li>
       *  <li>{@code toIndex > length}</li>
       *  <li>{@code length < 0}, which is implied from the former inequalities</li>
       * </ul>
       *
       * @param fromIndex the lower-bound (inclusive) of the sub-range
       * @param toIndex the upper-bound (exclusive) of the sub-range
       * @param length the upper-bound (exclusive) the range
       * @return {@code fromIndex} if the sub-range within bounds of the range
       * @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
       * @since 9
       */
      public static
      int checkFromToIndex(int fromIndex, int toIndex, int length) {
          return Preconditions.checkFromToIndex(fromIndex, toIndex, length, null);
      }
  
      /**
       * Checks if the sub-range from {@code fromIndex} (inclusive) to
       * {@code fromIndex + size} (exclusive) is within the bounds of range from
       * {@code 0} (inclusive) to {@code length} (exclusive).
       *
       * <p>The sub-range is defined to be out-of-bounds if any of the following
       * inequalities is true:
       * <ul>
       *  <li>{@code fromIndex < 0}</li>
       *  <li>{@code size < 0}</li>
       *  <li>{@code fromIndex + size > length}, taking into account integer overflow</li>
       *  <li>{@code length < 0}, which is implied from the former inequalities</li>
       * </ul>
       *
       * @param fromIndex the lower-bound (inclusive) of the sub-interval
       * @param size the size of the sub-range
       * @param length the upper-bound (exclusive) of the range
       * @return {@code fromIndex} if the sub-range within bounds of the range
       * @throws IndexOutOfBoundsException if the sub-range is out-of-bounds
       * @since 9
       */
      public static
      int checkFromIndexSize(int fromIndex, int size, int length) {
          return Preconditions.checkFromIndexSize(fromIndex, size, length, null);
      }
  
  }
  