/*
* 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 javax.annotation.Nullable;
/**
* 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: <pre> {@code
*
* public void checkKeyValue(Object key, Object value) {
* if (key == null || value == null) {
* throw new NullPointerException();
* }
* }}</pre>
*
* 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<K, V> {
/**
* 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();
}
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