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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 {
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
compare(Comparable<Object> c1, Comparable<Object> c2)51         public int compare(Comparable<Object> c1, Comparable<Object> c2) {
52             return c1.compareTo(c2);
53         }
54 
55         @Override
reversed()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         @java.io.Serial
66         private static final long serialVersionUID = -7569533591570686392L;
67         private final boolean nullFirst;
68         // if null, non-null Ts are considered equal
69         @SuppressWarnings("serial") // Not statically typed as Serializable
70         private final Comparator<T> real;
71 
72         @SuppressWarnings("unchecked")
NullComparator(boolean nullFirst, Comparator<? super T> real)73         NullComparator(boolean nullFirst, Comparator<? super T> real) {
74             this.nullFirst = nullFirst;
75             this.real = (Comparator<T>) real;
76         }
77 
78         @Override
compare(T a, T b)79         public int compare(T a, T b) {
80             if (a == null) {
81                 return (b == null) ? 0 : (nullFirst ? -1 : 1);
82             } else if (b == null) {
83                 return nullFirst ? 1: -1;
84             } else {
85                 return (real == null) ? 0 : real.compare(a, b);
86             }
87         }
88 
89         @Override
thenComparing(Comparator<? super T> other)90         public Comparator<T> thenComparing(Comparator<? super T> other) {
91             Objects.requireNonNull(other);
92             return new NullComparator<>(nullFirst, real == null ? other : real.thenComparing(other));
93         }
94 
95         @Override
reversed()96         public Comparator<T> reversed() {
97             return new NullComparator<>(!nullFirst, real == null ? null : real.reversed());
98         }
99     }
100 }
101