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 * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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 */
package java.util.function;

import java.util.Objects;

/**
 * Represents a function that accepts one argument and produces a result.
 *
 * <p>This is a <a href="package-summary.html">functional interface</a>
 * whose functional method is {@link #apply(Object)}.
 *
 * @param <T> the type of the input to the function
 * @param <R> the type of the result of the function
 *
 * @since 1.8
 */
@FunctionalInterface
public interface Function<T, R> {

 /**
 * Applies this function to the given argument.
 *
 * @param t the function argument
 * @return the function result
 */
 R apply(T t);

 /**
 * Returns a composed function that first applies the {@code before}
 * function to its input, and then applies this function to the result.
 * If evaluation of either function throws an exception, it is relayed to
 * the caller of the composed function.
 *
 * @param <V> the type of input to the {@code before} function, and to the
 * composed function
 * @param before the function to apply before this function is applied
 * @return a composed function that first applies the {@code before}
 * function and then applies this function
 * @throws NullPointerException if before is null
 *
 * @see #andThen(Function)
 */
 default <V> Function<V, R> compose(Function<? super V, ? extends T> before) {
 Objects.requireNonNull(before);
 return (V v) -> apply(before.apply(v));
 }

 /**
 * Returns a composed function that first applies this function to
 * its input, and then applies the {@code after} function to the result.
 * If evaluation of either function throws an exception, it is relayed to
 * the caller of the composed function.
 *
 * @param <V> the type of output of the {@code after} function, and of the
 * composed function
 * @param after the function to apply after this function is applied
 * @return a composed function that first applies this function and then
 * applies the {@code after} function
 * @throws NullPointerException if after is null
 *
 * @see #compose(Function)
 */
 default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) {
 Objects.requireNonNull(after);
 return (T t) -> after.apply(apply(t));
 }

 /**
 * Returns a function that always returns its input argument.
 *
 * @param <T> the type of the input and output objects to the function
 * @return a function that always returns its input argument
 */
 static <T> Function<T, T> identity() {
 return t -> t;
 }
}