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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code is distributed in the hope that it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

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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;

    }

}