State Pattern
Sometimes you find yourself in a Finite-State Machine problem, where an object has a few states that can interchange at anytime, and the object behaves differently according to each state.
Intent
Allow an object to alter its behavior when its internal state changes. The object will appear as if it changed its class.
When to use
When the object's behavior depends on its state and it must change its behavior at run-time depending on the state.
When you have a class polluted with massive conditionals that alter how the class behaves according to the current values of the class’s fields.
When you have a lot of duplicate code across similar states and transitions of a condition-based state machine.
Structure
Context: defines the interface of interest to the clients (usually it's directly a class that holds the state).
State: defines an interface for encapsulating the behavior associated with a particular state of the Context.
ConcreteState: they are the subclasses that implement the different behaviors.
Note
Applying this pattern can be overkill if a state machine has only a few states or rarely changes.
Examples
Source Code | UML |
// TODO |
You can find the tests here.
Last updated
