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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     final static 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")
NullComparator(boolean nullFirst, Comparator<? super T> real)71         NullComparator(boolean nullFirst, Comparator<? super T> real) {
72             this.nullFirst = nullFirst;
73             this.real = (Comparator<T>) real;
74         }
75 
76         @Override
compare(T a, T b)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
thenComparing(Comparator<? super T> other)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
reversed()94         public Comparator<T> reversed() {
95             return new NullComparator<>(!nullFirst, real == null ? null : real.reversed());
96         }
97     }
98 }
99