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      1 /*
      2  * Copyright (C) 2007 Google Inc.
      3  *
      4  * Licensed under the Apache License, Version 2.0 (the "License");
      5  * you may not use this file except in compliance with the License.
      6  * You may obtain a copy of the License at
      7  *
      8  * http://www.apache.org/licenses/LICENSE-2.0
      9  *
     10  * Unless required by applicable law or agreed to in writing, software
     11  * distributed under the License is distributed on an "AS IS" BASIS,
     12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
     13  * See the License for the specific language governing permissions and
     14  * limitations under the License.
     15  */
     16 
     17 package com.android.mail.lib.base;
     18 
     19 
     20 /**
     21  * Determines a true or false value for a given input. For example, a
     22  * {@code RegexPredicate} might implement {@code Predicate<String>}, and return
     23  * {@code true} for any string that matches its given regular expression.
     24  *
     25  * <p>Implementations which may cause side effects upon evaluation are strongly
     26  * encouraged to state this fact clearly in their API documentation.
     27  *
     28  * @author Kevin Bourrillion
     29  * @since 2010.01.04 <b>stable</b> (imported from Google Collections Library)
     30  */
     31 public interface Predicate<T> {
     32 
     33   /*
     34    * This interface does not extend Function<T, Boolean> because doing so would
     35    * let predicates return null.
     36    */
     37 
     38   /**
     39    * Applies this predicate to the given object.
     40    *
     41    * @param input the input that the predicate should act on
     42    * @return the value of this predicate when applied to the input {@code t}
     43    */
     44   boolean apply(T input);
     45 
     46   /**
     47    * Indicates whether some other object is equal to this {@code Predicate}.
     48    * This method can return {@code true} <i>only</i> if the specified object is
     49    * also a {@code Predicate} and, for every input object {@code input}, it
     50    * returns exactly the same value. Thus, {@code predicate1.equals(predicate2)}
     51    * implies that either {@code predicate1.apply(input)} and
     52    * {@code predicate2.apply(input)} are both {@code true} or both
     53    * {@code false}.
     54    *
     55    * <p>Note that it is always safe <i>not</i> to override
     56    * {@link Object#equals}.
     57    */
     58   boolean equals(Object obj);
     59 }
     60