1 /* 2 * Copyright (c) 2010, 2013, 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 argument, yielding an appropriate result. 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 the input to the {@code apply} operation 35 * @param <R> the type of the result of the {@code apply} operation 36 * 37 * @since 1.8 38 */ 39 @FunctionalInterface 40 public interface Function<T, R> { 41 42 /** 43 * Compute the result of applying the function to the input argument 44 * 45 * @param t the input object 46 * @return the function result 47 */ 48 R apply(T t); 49 50 /** 51 * Returns a new function which applies the provided function followed by 52 * this function. If either function throws an exception, it is relayed 53 * to the caller. 54 * 55 * @param <V> type of input objects to the combined function. May be the 56 * same type as {@code <T>} or {@code <R>} 57 * @param before an additional function to be applied before this function 58 * is applied 59 * @return a function which performs the provided function followed by this 60 * function 61 * @throws NullPointerException if before is null 62 */ 63 default <V> Function<V, R> compose(Function<? super V, ? extends T> before) { 64 Objects.requireNonNull(before); 65 return (V v) -> apply(before.apply(v)); 66 } 67 68 /** 69 * Returns a new function which applies this function followed by the 70 * provided function. If either function throws an exception, it is relayed 71 * to the caller. 72 * 73 * @param <V> type of output objects to the combined function. May be the 74 * same type as {@code <T>} or {@code <R>} 75 * @param after an additional function to be applied after this function is 76 * applied 77 * @return a function which performs this function followed by the provided 78 * function 79 * @throws NullPointerException if after is null 80 */ 81 default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) { 82 Objects.requireNonNull(after); 83 return (T t) -> after.apply(apply(t)); 84 } 85 86 /** 87 * Returns a {@code Function} whose {@code apply} method returns its input. 88 * 89 * @param <T> the type of the input and output objects to the function 90 * @return a {@code Function} whose {@code apply} method returns its input 91 */ 92 static <T> Function<T, T> identity() { 93 return t -> t; 94 } 95 }