001    /*
002     * Copyright (C) 2007 Google Inc.
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.collect;
018    
019    import com.google.common.annotations.Beta;
020    import com.google.common.annotations.GwtCompatible;
021    
022    import javax.annotation.Nullable;
023    
024    /**
025     * A constraint on the keys and values that may be added to a {@code Map} or
026     * {@code Multimap}. For example, {@link MapConstraints#notNull()}, which
027     * prevents a map from including any null keys or values, could be implemented
028     * like this: <pre>   {@code
029     *
030     *   public void checkKeyValue(Object key, Object value) {
031     *     if (key == null || value == null) {
032     *       throw new NullPointerException();
033     *     }
034     *   }}</pre>
035     *
036     * In order to be effective, constraints should be deterministic; that is, they
037     * should not depend on state that can change (such as external state, random
038     * variables, and time) and should only depend on the value of the passed-in key
039     * and value. A non-deterministic constraint cannot reliably enforce that all
040     * the collection's elements meet the constraint, since the constraint is only
041     * enforced when elements are added.
042     *
043     * @author Mike Bostock
044     * @see MapConstraints
045     * @see Constraint
046     * @since 3
047     */
048    @GwtCompatible
049    @Beta
050    public interface MapConstraint<K, V> {
051      /**
052       * Throws a suitable {@code RuntimeException} if the specified key or value is
053       * illegal. Typically this is either a {@link NullPointerException}, an
054       * {@link IllegalArgumentException}, or a {@link ClassCastException}, though
055       * an application-specific exception class may be used if appropriate.
056       */
057      void checkKeyValue(@Nullable K key, @Nullable V value);
058    
059      /**
060       * Returns a brief human readable description of this constraint, such as
061       * "Not null".
062       */
063      String toString();
064    }