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


public interface Constraint<E>

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

  public void checkElement(Object element) {
    if (element == 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 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.

Author:
Mike Bostock
See Also:
Constraints, MapConstraint

Method Summary
 void 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

void 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.


toString

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

Overrides:
toString in class Object