/*
* Copyright (C) 2007 Google Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.google.gdata.util.common.base;
import com.google.common.annotations.GwtCompatible;
import javax.annotation.Nullable;
/**
* Determines a true or false value for a given input. For example, a
* {@code RegexPredicate} might implement {@code Predicate<String>}, and return
* {@code true} for any string that matches its given regular expression.
*
* <p>Implementations which may cause side effects upon evaluation are strongly
* encouraged to state this fact clearly in their API documentation.
*
*
*/
@GwtCompatible
public interface Predicate<T> {
/*
* This interface does not extend Function<T, Boolean> because doing so would
* let predicates return null.
*/
/**
* Applies this predicate to the given object.
*
* @param input the input that the predicate should act on
* @return the value of this predicate when applied to the input {@code t}
*/
boolean apply(T input);
/**
* Indicates whether some other object is equal to this {@code Predicate}.
* This method can return {@code true} <i>only</i> if the specified object is
* also a {@code Predicate} and, for every input object {@code input}, it
* returns exactly the same value. Thus, {@code predicate1.equals(predicate2)}
* implies that either {@code predicate1.apply(input)} and
* {@code predicate2.apply(input)} are both {@code true} or both
* {@code false}.
*
* <p>Note that it is always safe <i>not</i> to override
* {@link Object#equals}.
*/
boolean equals(Object obj);
}