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 com.google.errorprone.annotations.CanIgnoreReturnValue;
019import javax.annotation.CheckForNull;
020import org.checkerframework.checker.nullness.qual.Nullable;
021
022/**
023 * Legacy version of {@link java.util.function.Predicate java.util.function.Predicate}. Determines a
024 * true or false value for a given input.
025 *
026 * <p>As this interface extends {@code java.util.function.Predicate}, an instance of this type may
027 * be used as a {@code Predicate} directly. To use a {@code java.util.function.Predicate} where a
028 * {@code com.google.common.base.Predicate} is expected, use the method reference {@code
029 * predicate::test}.
030 *
031 * <p>This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the
032 * appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible.
033 * Otherwise, at least reduce <i>explicit</i> dependencies on this type by using lambda expressions
034 * or method references instead of classes, leaving your code easier to migrate in the future.
035 *
036 * <p>The {@link Predicates} class provides common predicates and related utilities.
037 *
038 * <p>See the Guava User Guide article on <a
039 * href="https://github.com/google/guava/wiki/FunctionalExplained">the use of {@code Predicate}</a>.
040 *
041 * @author Kevin Bourrillion
042 * @since 2.0
043 */
044@FunctionalInterface
045@GwtCompatible
046@ElementTypesAreNonnullByDefault
047public interface Predicate<T extends @Nullable Object> extends java.util.function.Predicate<T> {
048  /**
049   * Returns the result of applying this predicate to {@code input} (Java 8 users, see notes in the
050   * class documentation above). This method is <i>generally expected</i>, but not absolutely
051   * required, to have the following properties:
052   *
053   * <ul>
054   *   <li>Its execution does not cause any observable side effects.
055   *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
056   *       Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
057   *       predicate.apply(b))}.
058   * </ul>
059   *
060   * @throws NullPointerException if {@code input} is null and this predicate does not accept null
061   *     arguments
062   */
063  @CanIgnoreReturnValue
064  boolean apply(@ParametricNullness T input);
065
066  /**
067   * Indicates whether another object is equal to this predicate.
068   *
069   * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
070   * However, an implementation may also choose to return {@code true} whenever {@code object} is a
071   * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable"
072   * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type
073   * {@code T}). Note that a {@code false} result from this method does not imply that the
074   * predicates are known <i>not</i> to be interchangeable.
075   */
076  @Override
077  boolean equals(@CheckForNull Object object);
078
079  @Override
080  default boolean test(@ParametricNullness T input) {
081    return apply(input);
082  }
083}