001/* 002 * Copyright (C) 2007 The Guava Authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except 005 * in compliance with the License. You may obtain a copy of the License at 006 * 007 * http://www.apache.org/licenses/LICENSE-2.0 008 * 009 * Unless required by applicable law or agreed to in writing, software distributed under the License 010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express 011 * or implied. See the License for the specific language governing permissions and limitations under 012 * the License. 013 */ 014 015package com.google.common.base; 016 017import com.google.common.annotations.GwtCompatible; 018import javax.annotation.CheckForNull; 019import org.checkerframework.checker.nullness.qual.Nullable; 020 021/** 022 * Legacy version of {@link java.util.function.Predicate java.util.function.Predicate}. Determines a 023 * true or false value for a given input. 024 * 025 * <p>As this interface extends {@code java.util.function.Predicate}, an instance of this type may 026 * be used as a {@code Predicate} directly. To use a {@code java.util.function.Predicate} where a 027 * {@code com.google.common.base.Predicate} is expected, use the method reference {@code 028 * predicate::test}. 029 * 030 * <p>This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the 031 * appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible. 032 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions 033 * or method references instead of classes, leaving your code easier to migrate in the future. 034 * 035 * <p>The {@link Predicates} class provides common predicates and related utilities. 036 * 037 * <p>See the Guava User Guide article on <a 038 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>. 039 * 040 * @author Kevin Bourrillion 041 * @since 2.0 042 */ 043@FunctionalInterface 044@GwtCompatible 045@ElementTypesAreNonnullByDefault 046public interface Predicate<T extends @Nullable Object> extends java.util.function.Predicate<T> { 047 /** 048 * Returns the result of applying this predicate to {@code input} (Java 8+ users, see notes in the 049 * class documentation above). This method is <i>generally expected</i>, but not absolutely 050 * required, to have the following properties: 051 * 052 * <ul> 053 * <li>Its execution does not cause any observable side effects. 054 * <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal 055 * Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) == 056 * predicate.apply(b))}. 057 * </ul> 058 * 059 * @throws NullPointerException if {@code input} is null and this predicate does not accept null 060 * arguments 061 */ 062 boolean apply(@ParametricNullness T input); 063 064 /** 065 * Indicates whether another object is equal to this predicate. 066 * 067 * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}. 068 * However, an implementation may also choose to return {@code true} whenever {@code object} is a 069 * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable" 070 * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type 071 * {@code T}). Note that a {@code false} result from this method does not imply that the 072 * predicates are known <i>not</i> to be interchangeable. 073 */ 074 @Override 075 boolean equals(@CheckForNull Object object); 076 077 @Override 078 default boolean test(@ParametricNullness T input) { 079 return apply(input); 080 } 081}