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 org.jspecify.annotations.Nullable;
019
020/**
021 * Legacy version of {@link java.util.function.Predicate java.util.function.Predicate}. Determines a
022 * true or false value for a given input.
023 *
024 * <p>As this interface extends {@code java.util.function.Predicate}, an instance of this type may
025 * be used as a {@code Predicate} directly. To use a {@code java.util.function.Predicate} where a
026 * {@code com.google.common.base.Predicate} is expected, use the method reference {@code
027 * predicate::test}.
028 *
029 * <p>This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the
030 * appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible.
031 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
032 * or method references instead of classes, leaving your code easier to migrate in the future.
033 *
034 * <p>The {@link Predicates} class provides common predicates and related utilities.
035 *
036 * <p>See the Guava User Guide article on <a
037 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>.
038 *
039 * @author Kevin Bourrillion
040 * @since 2.0
041 */
042@FunctionalInterface
043@GwtCompatible
044public interface Predicate<T extends @Nullable Object> extends java.util.function.Predicate<T> {
045  /**
046   * Returns the result of applying this predicate to {@code input} (Java 8+ users, see notes in the
047   * class documentation above). This method is <i>generally expected</i>, but not absolutely
048   * required, to have the following properties:
049   *
050   * <ul>
051   *   <li>Its execution does not cause any observable side effects.
052   *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
053   *       Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
054   *       predicate.apply(b))}.
055   * </ul>
056   *
057   * @throws NullPointerException if {@code input} is null and this predicate does not accept null
058   *     arguments
059   */
060  boolean apply(@ParametricNullness T input);
061
062  /**
063   * Indicates whether another object is equal to this predicate.
064   *
065   * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
066   * However, an implementation may also choose to return {@code true} whenever {@code object} is a
067   * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable"
068   * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type
069   * {@code T}). Note that a {@code false} result from this method does not imply that the
070   * predicates are known <i>not</i> to be interchangeable.
071   */
072  @Override
073  boolean equals(@Nullable Object object);
074
075  @Override
076  default boolean test(@ParametricNullness T input) {
077    return apply(input);
078  }
079}