/* * 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 javax.annotation.Nullable; import com.google.common.annotations.Beta; import com.google.common.annotations.GwtCompatible; /** * A constraint on the keys and values that may be added to a {@code Map} or * {@code Multimap}. For example, {@link MapConstraints#notNull()}, which * prevents a map from including any null keys or values, could be implemented * like this: * *
 *    {@code
 *
 *   public void checkKeyValue(Object key, Object value) {
 *     if (key == null || value == null) {
 *       throw new NullPointerException();
 *     }
 *   }}
 * 
* *

* 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 key * and value. 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. * * @author Mike Bostock * @see MapConstraints * @see Constraint * @since 3.0 */ @GwtCompatible @Beta public interface MapConstraint { /** * Throws a suitable {@code RuntimeException} if the specified key or value is * illegal. Typically this is either a {@link NullPointerException}, an * {@link IllegalArgumentException}, or a {@link ClassCastException}, though an * application-specific exception class may be used if appropriate. */ void checkKeyValue(@Nullable K key, @Nullable V value); /** * Returns a brief human readable description of this constraint, such as "Not * null". */ @Override String toString(); }