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 * Represents a function that accepts one argument and produces a result. 31 * 32 * <p>This is a <a href="package-summary.html">functional interface</a> 33 * whose functional method is {@link #apply(Object)}. 34 * 35 * @param <T> the type of the input to the function 36 * @param <R> the type of the result of the function 37 * 38 * @since 1.8 39 */ 40 @FunctionalInterface 41 public interface Function<T, R> { 42 43 /** 44 * Applies this function to the given argument. 45 * 46 * @param t the function argument 47 * @return the function result 48 */ 49 R apply(T t); 50 51 /** 52 * Returns a composed function that first applies the {@code before} 53 * function to its input, and then applies this function to the result. 54 * If evaluation of either function throws an exception, it is relayed to 55 * the caller of the composed function. 56 * 57 * @param <V> the type of input to the {@code before} function, and to the 58 * composed function 59 * @param before the function to apply before this function is applied 60 * @return a composed function that first applies the {@code before} 61 * function and then applies this function 62 * @throws NullPointerException if before is null 63 * 64 * @see #andThen(Function) 65 */ 66 default <V> Function<V, R> compose(Function<? super V, ? extends T> before) { 67 Objects.requireNonNull(before); 68 return (V v) -> apply(before.apply(v)); 69 } 70 71 /** 72 * Returns a composed function that first applies this function to 73 * its input, and then applies the {@code after} function to the result. 74 * If evaluation of either function throws an exception, it is relayed to 75 * the caller of the composed function. 76 * 77 * @param <V> the type of output of the {@code after} function, and of the 78 * composed function 79 * @param after the function to apply after this function is applied 80 * @return a composed function that first applies this function and then 81 * applies the {@code after} function 82 * @throws NullPointerException if after is null 83 * 84 * @see #compose(Function) 85 */ 86 default <V> Function<T, V> andThen(Function<? super R, ? extends V> after) { 87 Objects.requireNonNull(after); 88 return (T t) -> after.apply(apply(t)); 89 } 90 91 /** 92 * Returns a function that always returns its input argument. 93 * 94 * @param <T> the type of the input and output objects to the function 95 * @return a function that always returns its input argument 96 */ 97 static <T> Function<T, T> identity() { 98 return t -> t; 99 } 100 }