1 /*
   2  * Copyright (c) 2010, 2012 Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.util.function;
  26 
  27 import java.util.Objects;
  28 
  29 /**
  30  * Apply a function to the input object yielding an appropriate result object. A
  31  * function may variously provide a mapping between types, object instances or
  32  * keys and values or any other form of transformation upon the input.
  33  *
  34  * @param <T> the type of input objects to the {@code apply} operation
  35  * @param <R> the type of result objects from the {@code apply} operation. May
  36  * be the same type as {@code <T>}.
  37  *
  38  * @since 1.8
  39  */
  40 public interface Function<T, R> {
  41 
  42     /**
  43      * Yield an appropriate result object for the input object.
  44      *
  45      * @param t the input object
  46      * @return the function result
  47      */
  48     public R apply(T t);
  49 
  50     /**
  51      * Combine with another function returning a function which performs both
  52      * functions.
  53      *
  54      * @param <V> Type of output objects from the combined function. May be the
  55      * same type as {@code <U>}.
  56      * @param after An additional function to be applied to the result of this
  57      * function.
  58      * @return A function which performs both the original function followed by
  59      * a second function.
  60      */
  61     public default <V > Function<T, V> compose(Function<? super R, ? extends V> after) {
  62         Objects.requireNonNull(after);
  63         return (T t) -> after.apply(apply(t));
  64     }
  65 }