BinaryOperator.java revision 2278037aa1653a32014df55f325879b4fe75fc27 
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25package java.util.function;
26
27import java.util.Objects;
28import 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
46public 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     */
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     */
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