Recap: Flyweight Pattern

Flyweight stores the repeated part of many small objects once, and shares it.

• Intent. Use sharing to support large numbers of fine-grained objects efficiently.
• Two kinds of state. Intrinsic state is shared and lives in the flyweight; extrinsic state varies and is held or passed in by the client.
• Participants. The flyweight, which is immutable, the factory that pools flyweights by key, and the client.
• In the wild. Java's Integer.valueOf, which caches -128 to 127 by default and serves autoboxing.
• The trap. == on boxed integers is true inside the cache and false outside it; compare with equals.
• When not. A few hundred objects, state that must change per object, or code that relies on identity.