/* * 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; /** * 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 */ @Beta @GwtCompatible public interface Constraint