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.

Real world examples:

• java.lang.Integer#valueOf(int)

Credits

• Design Patterns: Elements of Reusable Object-Oriented Software