State

Allow an object to alter its behavior when its internal state changes. The object will appear to change its class.

Applicability

• Need to change an object's behavior when it changes its state
• Operations have large, multipart conditional statements that depend on the object's state

Consequences

• Localizes state-specific behavior and partitions behavior for different states
• Makes state transitions explicit
• State objects can be shared if they have no intrinsic state (see Flyweight).