/*

 * Copyright (c) 2012, 2019, 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

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package java.util;

import java.io.Serializable;

import java.util.function.BinaryOperator;

import java.util.function.Function;

import java.util.function.ToDoubleFunction;

import java.util.function.ToIntFunction;

import java.util.function.ToLongFunction;

/**

 * Package private supporting class for {@link Comparator}.

 */

class Comparators {

    private Comparators() {

        throw new AssertionError("no instances");

    }

    /**

     * Compares {@link Comparable} objects in natural order.

     *

     * @see Comparable

     */

    enum NaturalOrderComparator implements Comparator<Comparable<Object>> {

        INSTANCE;

        @Override

        public int compare(Comparable<Object> c1, Comparable<Object> c2) {

            return c1.compareTo(c2);

        }

        @Override

        public Comparator<Comparable<Object>> reversed() {

            return Comparator.reverseOrder();

        }

    }

    /**

     * Null-friendly comparators

     */

    static final class NullComparator<T> implements Comparator<T>, Serializable {

        @java.io.Serial

        private static final long serialVersionUID = -7569533591570686392L;

        private final boolean nullFirst;

        // if null, non-null Ts are considered equal

        @SuppressWarnings("serial") // Not statically typed as Serializable

        private final Comparator<T> real;

        @SuppressWarnings("unchecked")

        NullComparator(boolean nullFirst, Comparator<? super T> real) {

            this.nullFirst = nullFirst;

            this.real = (Comparator<T>) real;

        }

        @Override

        public int compare(T a, T b) {

            if (a == null) {

                return (b == null) ? 0 : (nullFirst ? -1 : 1);

            } else if (b == null) {

                return nullFirst ? 1: -1;

            } else {

                return (real == null) ? 0 : real.compare(a, b);

            }

        }

        @Override

        public Comparator<T> thenComparing(Comparator<? super T> other) {

            Objects.requireNonNull(other);

            return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other));

        }

        @Override

        public Comparator<T> reversed() {

            return new NullComparator<>(!nullFirst, real == null ? null : real.reversed());

        }

    }

}