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   * Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
   * 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.
   *
   * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   * or visit www.oracle.com if you need additional information or have any
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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;
      }
  }
  