MapConstraint

com.google.common.collect

Interface MapConstraint<K,V>

```
@GwtCompatible
 @Beta
public interface MapConstraint<K,V>
```
A constraint on the keys and values that may be added to a Map or Multimap. For example, MapConstraints.notNull(), which prevents a map from including any null keys or values, could be implemented like this:
```
    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.
Since:

3.0

See Also:

MapConstraints, Constraint

Method Summary

All Methods

Instance Methods

Abstract Methods
Modifier and Type	Method and Description
`void`	`checkKeyValue(K key, V value)` Throws a suitable `RuntimeException` if the specified key or value is illegal.
`String`	`toString()` Returns a brief human readable description of this constraint, such as "Not null".

- Method Detail
  - checkKeyValue
```
void checkKeyValue(K key,
                   V value)
```
    Throws a suitable RuntimeException if the specified key or value is illegal. Typically this is either a NullPointerException, an IllegalArgumentException, or a ClassCastException, though an application-specific exception class may be used if appropriate.
  - toString
```
String toString()
```
    Returns a brief human readable description of this constraint, such as "Not null".