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25 package java.util.function;
26 
27 import java.util.Objects;
28 import java.util.Comparator;
29 
30 /**
31  * Represents an operation upon two operands of the same type, producing a result
32  * of the same type as the operands.  This is a specialization of
33  * {@link BiFunction} for the case where the operands and the result are all of
34  * the same type.
35  *
36  * <p>This is a <a href="package-summary.html">functional interface</a>
37  * whose functional method is {@link #apply(Object, Object)}.
38  *
39  * @param <T> the type of the operands and result of the operator
40  *
41  * @see BiFunction
42  * @see UnaryOperator
43  * @since 1.8
44  */
45 @FunctionalInterface
46 public interface BinaryOperator<T> extends BiFunction<T,T,T> {
47     /**
48      * Returns a {@link BinaryOperator} which returns the lesser of two elements
49      * according to the specified {@code Comparator}.
50      *
51      * @param <T> the type of the input arguments of the comparator
52      * @param comparator a {@code Comparator} for comparing the two values
53      * @return a {@code BinaryOperator} which returns the lesser of its operands,
54      *         according to the supplied {@code Comparator}
55      * @throws NullPointerException if the argument is null
56      */
minBy(Comparator<? super T> comparator)57     public static <T> BinaryOperator<T> minBy(Comparator<? super T> comparator) {
58         Objects.requireNonNull(comparator);
59         return (a, b) -> comparator.compare(a, b) <= 0 ? a : b;
60     }
61 
62     /**
63      * Returns a {@link BinaryOperator} which returns the greater of two elements
64      * according to the specified {@code Comparator}.
65      *
66      * @param <T> the type of the input arguments of the comparator
67      * @param comparator a {@code Comparator} for comparing the two values
68      * @return a {@code BinaryOperator} which returns the greater of its operands,
69      *         according to the supplied {@code Comparator}
70      * @throws NullPointerException if the argument is null
71      */
maxBy(Comparator<? super T> comparator)72     public static <T> BinaryOperator<T> maxBy(Comparator<? super T> comparator) {
73         Objects.requireNonNull(comparator);
74         return (a, b) -> comparator.compare(a, b) >= 0 ? a : b;
75     }
76 }
77