Interface Constraint<E>


  • @GwtCompatible
    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.

    • Method Summary

      All Methods Instance Methods Abstract Methods 
      Modifier and Type Method Description
      E checkElement​(E element)
      Throws a suitable RuntimeException if the specified element is illegal.
      java.lang.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

        java.lang.String toString()
        Returns a brief human readable description of this constraint, such as "Not null" or "Positive number".
        Overrides:
        toString in class java.lang.Object