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/*
* Copyright (C) 2007 The Guava Authors
*
* 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.common.base;
import com.google.common.annotations.GwtCompatible;
import javax.annotation.CheckForNull;
import org.checkerframework.checker.nullness.qual.Nullable;
/**
* Determines a true or false value for a given input; a pre-Java-8 version of {@link
* java.util.function.Predicate java.util.function.Predicate}.
*
* The {@link Predicates} class provides common predicates and related utilities.
*
*
See the Guava User Guide article on the use of {@code Predicate}.
*
*
For Java 8+ users
*
* This interface is now a legacy type. Use {@code java.util.function.Predicate} (or the
* appropriate primitive specialization such as {@code IntPredicate}) instead whenever possible.
* Otherwise, at least reduce explicit dependencies on this type by using lambda expressions
* or method references instead of classes, leaving your code easier to migrate in the future.
*
*
To use a reference of this type (say, named {@code guavaPredicate}) in a context where {@code
* java.util.function.Predicate} is expected, use the method reference {@code
* guavaPredicate::apply}. For the other direction, use {@code javaUtilPredicate::test}. A future
* version of this interface will be made to extend {@code java.util.function.Predicate}, so
* that conversion will be necessary in only one direction. At that time, this interface will be
* officially discouraged.
*
* @author Kevin Bourrillion
* @since 2.0
*/
@GwtCompatible
@ElementTypesAreNonnullByDefault
public interface Predicate {
/**
* Returns the result of applying this predicate to {@code input} (Java 8 users, see notes in the
* class documentation above). This method is generally expected, but not absolutely
* required, to have the following properties:
*
*
* - Its execution does not cause any observable side effects.
*
- The computation is consistent with equals; that is, {@link Objects#equal
* Objects.equal}{@code (a, b)} implies that {@code predicate.apply(a) ==
* predicate.apply(b))}.
*
*
* @throws NullPointerException if {@code input} is null and this predicate does not accept null
* arguments
*/
boolean apply(@ParametricNullness T input);
/**
* Indicates whether another object is equal to this predicate.
*
* Most implementations will have no reason to override the behavior of {@link Object#equals}.
* However, an implementation may also choose to return {@code true} whenever {@code object} is a
* {@link Predicate} that it considers interchangeable with this one. "Interchangeable"
* typically means that {@code this.apply(t) == that.apply(t)} for all {@code t} of type
* {@code T}). Note that a {@code false} result from this method does not imply that the
* predicates are known not to be interchangeable.
*/
@Override
boolean equals(@CheckForNull Object object);
}