Design Pattern

Design Pattern

1. Flyweight

   • Why to use?
     • Reduce memory usage by sharing as much data as possible
   • When to use?
     • The flyweight object’s state is made up of an invariant component shared with other similar objects (intrinsic) and a variant component which can be manipulated by the client code (extrinsic)
   • How to implement?
     • To define an interface
     • To create the concrete classes
     • To create a factory class that will return build the flyweight object
     • It’s very important that the flyweight objects are immutable: any operation on the state must be performed by the factory.
     • The client will use the interface and the factory class to build the flyweight

2. Proxy

   • Why to use?
     • Surrogate or placeholder a real object expensive to create
   • When to use?
     • Lazy initialization (virtual proxy). This is when you have a heavyweight service object that wastes system resources by being always up, even though you only need it from time to time.
     • Access control (protection proxy). This is when you want only specific clients to be able to use the service object; for instance, when your objects are crucial parts of an operating system and clients are various launched applications (including malicious ones).
     • Local execution of a remote service (remote proxy). This is when the service object is located on a remote server.
     • Logging requests (logging proxy). This is when you want to keep a history of requests to the service object.
     • Caching request results (caching proxy). This is when you need to cache results of client requests and manage the life cycle of this cache, especially if results are quite large.
   • How to implement?
     • Implements the same interface of the real object
     • Wrappes the real object