Flyweight

Static diagram :

Description :

Type :

St (Structural)

Intent :

Use sharing to support large numbers of fine-grained objects efficiently.

Applicability :

The Flyweight pattern's effectiveness depends heavily on how and where it's used. Apply the Flyweight pattern when all of the following are true :
- An application uses a large number of objects.
- Storage costs are high because of the sheer quantity of objects.
- Most object state can be made extrinsic.
- Many groups of objects may be replaced by relatively few shared objects once extrinsic state is removed.
- The application doesn't depend on object identity. Since flyweight objects may be shared, identity tests will return true for conceptually distinct objects.

Pattern's participants :

Flyweight
Declares an interface through which flyweights can receive and act on extrinsic state.
ConcreteFlyweight
Implements the Flyweight interface and adds storage for intrinsic state, if any. A ConcreteFlyweight object must be sharable. Any state it stores must be intrinsic; that is, it must be independent of the ConcreteFlyweight object's context.
UnsharedConcreteFlyweight
Not all Flyweight subclasses need to be shared. The Flyweight interface enables sharing; it doesn't enforce it. It's common for UnsharedConcreteFlyweight objects to have ConcreteFlyweight objects as children at some level in the flyweight object structure.
FlyweightFactory
Creates and manages flyweight objects.
Ensures that flyweights are shared properly. When a client requests a flyweight, the FlyweightFactory object supplies an existing instance or creates one, if none exists.
Client
Maintains a reference to flyweight(s).
Computes or stores the extrinsic state of flyweight(s).

Problems :

1. Limiter le nombre d'objets en mémoire

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Design patterns

Flyweight

Static diagram :

Description :

Pattern's participants :

Problems :