/* * 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.collect; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; import com.google.common.base.Preconditions; /** * A constraint that an element must satisfy in order to be added to a * collection. For example, {@link Constraints#notNull()}, which prevents a * collection from including any null elements, could be implemented like this: *
{@code * * public Object checkElement(Object element) { * if (element == null) { * throw new NullPointerException(); * } * return element; * }}* *
In order to be effective, constraints should be deterministic; that is,
* they should not depend on state that can change (such as external state,
* random variables, and time) and should only depend on the value of the
* passed-in element. A non-deterministic constraint cannot reliably enforce
* that all the collection's elements meet the constraint, since the constraint
* is only enforced when elements are added.
*
* @see Constraints
* @see MapConstraint
* @author Mike Bostock
* @since 3.0
* @deprecated Use {@link Preconditions} for basic checks. In place of
* constrained collections, we encourage you to check your preconditions
* explicitly instead of leaving that work to the collection implementation.
* For the specific case of rejecting null, consider the immutable
* collections.
* This interface is scheduled for removal in Guava 16.0.
*/
@Beta
@Deprecated
@GwtCompatible
public
interface Constraint