Design Patterns Java™ Workbook

Summary

Generally speaking, the state of an object depends on the collective value of the object's instance variables. In some cases, an object's state can be a prominent aspect of a class's behavior. This often occurs when an object is modeling a real-world entity whose state is important. In such a situation, complex logic that depends on the object's state may appear in many methods. You can simplify such code by moving state-specific behavior to a hierarchy of state objects. This lets each state class contain the behavior for one state in the domain. It also allows the state classes to correspond directly to states in a state machine.

To handle transitions between states, you can let states retain a context reference that contains a set of ...