1 /*

     2  * Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.

     3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

     4  *

     5  * This code is free software; you can redistribute it and/or modify it

     6  * under the terms of the GNU General Public License version 2 only, as

     7  * published by the Free Software Foundation.  Oracle designates this

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

     9  * by Oracle in the LICENSE file that accompanied this code.

    10  *

    11  * This code is distributed in the hope that it will be useful, but WITHOUT

    12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

    13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

    14  * version 2 for more details (a copy is included in the LICENSE file that

    15  * accompanied this code).

    16  *

    17  * You should have received a copy of the GNU General Public License version

    18  * 2 along with this work; if not, write to the Free Software Foundation,

    19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

    20  *

    21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

    22  * or visit www.oracle.com if you need additional information or have any

    23  * questions.

    24  */

    25 package java.util;

    26 

    27 import java.io.Serializable;

    28 import java.util.function.BinaryOperator;

    29 import java.util.function.Function;

    30 import java.util.function.ToDoubleFunction;

    31 import java.util.function.ToIntFunction;

    32 import java.util.function.ToLongFunction;

    33 

    34 /**

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

    36  */

    37 class Comparators {

    38     private Comparators() {

    39         throw new AssertionError("no instances");

    40     }

    41 

    42     /**

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

    44      *

    45      * @see Comparable

    46      */

    47     enum NaturalOrderComparator implements Comparator<Comparable<Object>> {

    48         INSTANCE;

    49 

    50         @Override

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

    52             return c1.compareTo(c2);

    53         }

    54 

    55         @Override

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

    57             return Comparator.reverseOrder();

    58         }

    59     }

    60 

    61     /**

    62      * Null-friendly comparators

    63      */

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

    65         private static final long serialVersionUID = -7569533591570686392L;

    66         private final boolean nullFirst;

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

    68         private final Comparator<T> real;

    69 

    70         @SuppressWarnings("unchecked")

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

    72             this.nullFirst = nullFirst;

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

    74         }

    75 

    76         @Override

    77         public int compare(T a, T b) {

    78             if (a == null) {

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

    80             } else if (b == null) {

    81                 return nullFirst ? 1: -1;

    82             } else {

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

    84             }

    85         }

    86 

    87         @Override

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

    89             Objects.requireNonNull(other);

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

    91         }

    92 

    93         @Override

    94         public Comparator<T> reversed() {

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

    96         }

    97     }

    98 }