1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package com.google.common.base; 18 19 import com.google.common.annotations.GwtCompatible; 20 21 import javax.annotation.Nullable; 22 23 /** 24 * Determines an output value based on an input value. 25 * 26 * <p>The {@link Functions} class provides common functions and related utilites. 27 * 28 * <p>See the Guava User Guide article on <a href= 29 * "http://code.google.com/p/guava-libraries/wiki/FunctionalExplained">the use of {@code 30 * Function}</a>. 31 * 32 * @author Kevin Bourrillion 33 * @since 2.0 (imported from Google Collections Library) 34 */ 35 @GwtCompatible 36 public interface Function<F, T> { 37 /** 38 * Returns the result of applying this function to {@code input}. This method is <i>generally 39 * expected</i>, but not absolutely required, to have the following properties: 40 * 41 * <ul> 42 * <li>Its execution does not cause any observable side effects. 43 * <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal 44 * Objects.equal}{@code (a, b)} implies that {@code Objects.equal(function.apply(a), 45 * function.apply(b))}. 46 * </ul> 47 * 48 * @throws NullPointerException if {@code input} is null and this function does not accept null 49 * arguments 50 */ 51 @Nullable T apply(@Nullable F input); 52 53 /** 54 * Indicates whether another object is equal to this function. 55 * 56 * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}. 57 * However, an implementation may also choose to return {@code true} whenever {@code object} is a 58 * {@link Function} that it considers <i>interchangeable</i> with this one. "Interchangeable" 59 * <i>typically</i> means that {@code Objects.equal(this.apply(f), that.apply(f))} is true for all 60 * {@code f} of type {@code F}. Note that a {@code false} result from this method does not imply 61 * that the functions are known <i>not</i> to be interchangeable. 62 */ 63 @Override 64 boolean equals(@Nullable Object object); 65 } 66
