随笔档案

A factory method handles object creation and encapsulates it in a subclass. This decouples the client code in the superclass from the object creation code in the subclass.
1. A factory method is abstract so the subclasses are counted on to handle object creation.
2. A factory method returns a Product that is typically used within methods defined in the superclass.
3. A factory method isolates the client from knowing what kind of concrete Product is actually created.
4. A factory method may be parameterized(or not) to select among several variations of a product.