jdk/src/share/classes/java/util/function/BiFunction.java

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * particular file as subject to the "Classpath" exception as provided
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 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
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package java.util.function;

import java.util.Objects;

/**
 * Apply a function to the input arguments, yielding an appropriate result. This
 * is the two-arity specialization of {@link Function}. A function may
 * variously provide a mapping between types, object instances or keys and
 * values or any other form of transformation upon the input.
 *
 * @param <T> the type of the first argument to the {@code apply} operation
 * @param <U> the type of the second argument to the {@code apply} operation
 * @param <R> the type of results returned by the {@code apply} operation
 *
 * @see Function
 * @since 1.8
 */
@FunctionalInterface
public interface BiFunction<T, U, R> {

    /**
     * Compute the result of applying the function to the input arguments
     *
     * @param t an input object
     * @param u an input object
     * @return the function result
     */
    R apply(T t, U u);

    /**
     * Returns a new function which applies this function followed by the
     * provided function.  If either function throws an exception, it is relayed
     * to the caller.
     *
     * @param <V> Type of output objects to the combined function. May be the
     * same type as {@code <T>}, {@code <U>} or {@code <R>}
     * @param after An additional function to be applied after this function is
     * applied
     * @return A function which performs this function followed by the provided
     * function
     * @throws NullPointerException if after is null
     */
    default <V> BiFunction<T, U, V> andThen(Function<? super R, ? extends V> after) {
        Objects.requireNonNull(after);
        return (T t, U u) -> after.apply(apply(t, u));
    }
}