1 /* 2 * Copyright (C) 2007 The Guava Authors 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 5 * in compliance with the License. You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software distributed under the License 10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 11 * or implied. See the License for the specific language governing permissions and limitations under 12 * the License. 13 */ 14 15 package com.google.common.base; 16 17 import com.google.common.annotations.GwtCompatible; 18 import com.google.errorprone.annotations.CanIgnoreReturnValue; 19 import org.checkerframework.checker.nullness.qual.Nullable; 20 21 /** 22 * Legacy version of {@link java.util.function.Predicate java.util.function.Predicate}. Determines a 23 * true or false value for a given input. 24 * 25 * <p>As this interface extends {@code java.util.function.Predicate}, an instance of this type may 26 * be used as a {@code Predicate} directly. To use a {@code java.util.function.Predicate} where a 27 * {@code com.google.common.base.Predicate} is expected, use the method reference {@code 28 * predicate::test}. 29 * 30 * <p>This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the 31 * appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible. 32 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions 33 * or method references instead of classes, leaving your code easier to migrate in the future. 34 * 35 * <p>The {@link Predicates} class provides common predicates and related utilities. 36 * 37 * <p>See the Guava User Guide article on <a 38 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>. 39 * 40 * @author Kevin Bourrillion 41 * @since 2.0 42 */ 43 @FunctionalInterface 44 @GwtCompatible 45 public interface Predicate<T> extends java.util.function.Predicate<T> { 46 /** 47 * Returns the result of applying this predicate to {@code input} (Java 8 users, see notes in the 48 * class documentation above). This method is <i>generally expected</i>, but not absolutely 49 * required, to have the following properties: 50 * 51 * <ul> 52 * <li>Its execution does not cause any observable side effects. 53 * <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal 54 * Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) == 55 * predicate.apply(b))}. 56 * </ul> 57 * 58 * @throws NullPointerException if {@code input} is null and this predicate does not accept null 59 * arguments 60 */ 61 @CanIgnoreReturnValue apply(@ullable T input)62 boolean apply(@Nullable T input); 63 64 /** 65 * Indicates whether another object is equal to this predicate. 66 * 67 * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}. 68 * However, an implementation may also choose to return {@code true} whenever {@code object} is a 69 * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable" 70 * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type 71 * {@code T}). Note that a {@code false} result from this method does not imply that the 72 * predicates are known <i>not</i> to be interchangeable. 73 */ 74 @Override equals(@ullable Object object)75 boolean equals(@Nullable Object object); 76 77 @Override test(@ullable T input)78 default boolean test(@Nullable T input) { 79 return apply(input); 80 } 81 } 82