Behavioral Patterns : Null Object

Properties:

-          Simply providing a do-nothing implementation of a particular interface.

-          Concrete class does nothing, all requests are effectively ignored.

Implementation:

-          AbstractOperation declares operations.

-          RealOperation  implements AbstractOperation and defines operations.

-          NullOperation  implements AbstractOperation and leaves operations empty.

-          Client executes operations on AbstractOperation, does not care about if implemantation is real or null.

Java Standard Library Implementations:

-          java.util.Collections#emptyList()

-          java.util.Collections#emptyMap()

-          java.util.Collections#emptySet()

Example Usage:

@Override

public List<T> findAll(int maxResults) {

   

    if (maxResults == 0)

        return Collections.emptyList(); // return empty list

    Query query = getSession().createQuery("SELECT p FROM Person p");

   

    return query.setFirstResult(0).setMaxResults(maxResults).list();

}