1 /*
   2  * Copyright (c) 2010, 2011, 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 objects yielding an appropriate result object.
  31  * A 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 <R> the type of output objects from {@code apply} operation.
  35  * @param <T> the type of input objects provided to the {@code apply} operation.
  36  * @param <U> the type of input objects provided to the {@code apply} operation.
  37  */
  38 public interface BiFunction<T, U, R> {
  39 
  40     /**
  41      * Map the provided input objects to an appropriate output object.
  42      *
  43      * @param t an input object
  44      * @param u an input object
  45      * @return the function result
  46      */
  47     R apply(T t, U u);
  48 
  49     /**
  50      * Combine with another function producing a function which performs both
  51      * operations.
  52      *
  53      * @param <W> Type of output objects from the combined function. May be the
  54      * same type as {@code <U>}.
  55      * @param after An additional function to be applied to the result of this
  56      * function.
  57      * @return A function which performs both the original function followed by
  58      * a second function.
  59      */
  60     public default <W> BiFunction<T, U, W> compose(Function<? super R, ? extends W> after) {
  61         Objects.requireNonNull(after);
  62         return (T t, U u) -> after.apply(apply(t, u));
  63     }
  64 }