/* * 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 * questions. */ package java.util.function; import java.util.Objects; /** * Apply a function to the input argument, yielding an appropriate result. A * function may variously provide a mapping between types, object instances or * keys and values or any other form of transformation upon the input. * * @param the type of the input to the {@code apply} operation * @param the type of the result of the {@code apply} operation * * @since 1.8 */ @FunctionalInterface public interface Function { /** * Compute the result of applying the function to the input argument * * @param t the input object * @return the function result */ R apply(T t); /** * Returns a new function which applies the provided function followed by * this function. If either function throws an exception, it is relayed * to the caller. * * @param type of input objects to the combined function. May be the * same type as {@code } or {@code } * @param before an additional function to be applied before this function * is applied * @return a function which performs the provided function followed by this * function * @throws NullPointerException if before is null */ default Function compose(Function before) { Objects.requireNonNull(before); return (V v) -> apply(before.apply(v)); } /** * Returns a new function which applies this function followed by the * provided function. If either function throws an exception, it is relayed * to the caller. * * @param type of output objects to the combined function. May be the * same type as {@code } or {@code } * @param after an additional function to be applied after this function is * applied * @return a function which performs this function followed by the provided * function * @throws NullPointerException if after is null */ default Function andThen(Function after) { Objects.requireNonNull(after); return (T t) -> after.apply(apply(t)); } /** * Returns a {@code Function} whose {@code apply} method returns its input. * * @param the type of the input and output objects to the function * @return a {@code Function} whose {@code apply} method returns its input */ static Function identity() { return t -> t; } }