1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 * http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17 package com.google.common.collect;
18
19 import com.google.common.annotations.Beta;
20 import com.google.common.annotations.GwtCompatible;
21
22 import javax.annotation.Nullable;
23
24 /**
25 * A constraint on the keys and values that may be added to a {@code Map} or
26 * {@code Multimap}. For example, {@link MapConstraints#notNull()}, which
27 * prevents a map from including any null keys or values, could be implemented
28 * like this: <pre> {@code
29 *
30 * public void checkKeyValue(Object key, Object value) {
31 * if (key == null || value == null) {
32 * throw new NullPointerException();
33 * }
34 * }}</pre>
35 *
36 * <p>In order to be effective, constraints should be deterministic; that is, they
37 * should not depend on state that can change (such as external state, random
38 * variables, and time) and should only depend on the value of the passed-in key
39 * and value. A non-deterministic constraint cannot reliably enforce that all
40 * the collection's elements meet the constraint, since the constraint is only
41 * enforced when elements are added.
42 *
43 * @author Mike Bostock
44 * @see MapConstraints
45 * @see Constraint
46 * @since 3.0
47 */
48 @GwtCompatible
49 @Beta
50 public interface MapConstraint<K, V> {
51 /**
52 * Throws a suitable {@code RuntimeException} if the specified key or value is
53 * illegal. Typically this is either a {@link NullPointerException}, an
54 * {@link IllegalArgumentException}, or a {@link ClassCastException}, though
55 * an application-specific exception class may be used if appropriate.
56 */
57 void checkKeyValue(@Nullable K key, @Nullable V value);
58
59 /**
60 * Returns a brief human readable description of this constraint, such as
61 * "Not null".
62 */
63 @Override
64 String toString();
65 }