com.google.common.collect
Interface Constraint<E>

@Beta
@GwtCompatible
public interface Constraint<E>

A constraint that an element must satisfy in order to be added to a collection. For example, Constraints.notNull(), which prevents a collection from including any null elements, could be implemented like this:

   public Object checkElement(Object element) {
     if (element == null) {
       throw new NullPointerException();
     }
     return element;
   }

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 element. 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

Author:

Mike Bostock

See Also:

Constraints, MapConstraint

Method Summary

E	checkElement(E element) Throws a suitable RuntimeException if the specified element is illegal.
String	toString() Returns a brief human readable description of this constraint, such as "Not null" or "Positive number".

Method Detail

checkElement

E checkElement(E element)

Throws a suitable RuntimeException if the specified element is illegal. Typically this is either a NullPointerException, an IllegalArgumentException, or a ClassCastException, though an application-specific exception class may be used if appropriate.

Parameters:

element - the element to check

Returns:

the provided element

toString

String toString()

Returns a brief human readable description of this constraint, such as "Not null" or "Positive number".

Overrides:

toString in class Object