Implementation Issues

• Different Kinds of Operations
  
  • "To reuse an abstract class effectively, subclass writers must understand which operations are designed for overriding." [GoF, p328]
  • Primitive operations - abstract operations that must be implemented by subclasses; or concrete operations that provide a default implementation and can be redefined by subclasses if necessary.
    Primitive operations can be declared protected to enable subclassing over package boundaries but keeping clients from calling them directly (see Sample Code).
  • Final operations - concrete operations that can not be overridden by subclasses.
  • Hook operations - concrete operations that do nothing by default and can be redefined by subclasses if necessary.
  • Template methods themselves can be declared final so that they can not be overridden.