It is possible to apply a design pattern on an existing class. For instance, if you want to apply the Singleton design pattern on a class named PrinterManager:
Design patterns are categorized as creational, structural or
behavioral
design patterns. The following design patterns are currently
supported:
Creational
Structural
Behavioral
Factory Method
Prototype
SingletonAdapter
Composite
ProxyChain of Responsibility
Command
Iterator
Observer
State
Strategy
Template Method