What and When Design Pattern?

 

Pattern	What & When
Decorator	To provide a way of attaching new state and behavior to an object dynamically. This pattern allows to add new functionality an existing object without altering its structure by creating wrapper class. You have: An existing component class that may be unavailable for subclassing You wants: Attach additional state and behavior to an object dynamically. Make changes to some objects in a class without affecting others. Avoid subclassing because too many classes could result.
****************** Proxy	It Supports objects that control the creation of and access to other objects In Proxy pattern, a class represents functionality of another class. You have: Are expensive to create Need access control Access remote sites. Need to perform some actions when they are accessed. You wants: Create objects when their operations are requested. Perform checks on objects whenever accessed. Have a local objects that will refers to a remote object. Implement access rights on objects as their operation are requested.
****************** Bridge	It decouples an abstraction from its implementation, enabling them to vary independently. You have: Identify that there are operations that do not always need to be implemented in the same way. You wants: Completely hide implementation from client. Combine different part of system at runtime.