    001    /*
    002     * Copyright (C) 2007 The Guava Authors
    003     *
    004     * Licensed under the Apache License, Version 2.0 (the "License");
    005     * you may not use this file except in compliance with the License.
    006     * You may obtain a copy of the License at
    007     *
    008     * http://www.apache.org/licenses/LICENSE-2.0
    009     *
    010     * Unless required by applicable law or agreed to in writing, software
    011     * distributed under the License is distributed on an "AS IS" BASIS,
    012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    013     * See the License for the specific language governing permissions and
    014     * limitations under the License.
    015     */
    016
    017    package com.google.common.base;
    018
    019    import com.google.common.annotations.GwtCompatible;
    020
    021    import javax.annotation.Nullable;
    022
    023    /**
    024     * Determines a true or false value for a given input.
    025     *
    026     * @author Kevin Bourrillion
    027     * @since 2.0 (imported from Google Collections Library)
    028     */
    029    @GwtCompatible
    030    public interface Predicate<T> {
    031      /**
    032       * Returns the result of applying this predicate to {@code input}. This method is <i>generally
    033       * expected</i>, but not absolutely required, to have the following properties:
    034       *
    035       * <ul>
    036       * <li>Its execution does not cause any observable side effects.
    037       * <li>The computation is <i>consistent with equals</i>; that is, {@link Objects#equal
    038       *     Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
    039       *     predicate.apply(b))}.
    040       * </ul>
    041       *
    042       * @throws NullPointerException if {@code input} is null and this predicate does not accept null
    043       *     arguments
    044       */
    045      boolean apply(@Nullable T input);
    046
    047      /**
    048       * Indicates whether another object is equal to this predicate.
    049       *
    050       * <p>Most implementations will have no reason to override the behavior of {@link Object#equals}.
    051       * However, an implementation may also choose to return {@code true} whenever {@code object} is a
    052       * {@link Predicate} that it considers <i>interchangeable</i> with this one. "Interchangeable"
    053       * <i>typically</i> means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type
    054       * {@code T}). Note that a {@code false} result from this method does not imply that the
    055       * predicates are known <i>not</i> to be interchangeable.
    056       */
    057      @Override
    058      boolean equals(@Nullable Object object);
    059    }