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 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
045public interface Predicate<T> extends java.util.function.Predicate<T> {
046  /**
047   * Returns the result of applying this predicate to {@code input} (Java 8 users, see notes in the
048   * class documentation above). This method is <i>generally expected</i>, but not absolutely
049   * required, to have the following properties:
050   *
051   * <ul>
052   *   <li>Its execution does not cause any observable side effects.
053   *   <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
054   *       Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
055   *       predicate.apply(b))}.
056   * </ul>
057   *
058   * @throws NullPointerException if {@code input} is null and this predicate does not accept null
059   *     arguments
060   */
061  @CanIgnoreReturnValue
062  boolean apply(@Nullable 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(@Nullable Object object);
076
077  @Override
078  default boolean test(@Nullable T input) {
079    return apply(input);
080  }
081}