State design pattern
The State design pattern encapsulates state-specific behavior in separate representations and delegates an object's behavior according to its current state.
Object-Oriented Software Design in C++
A behavioral design pattern that encapsulates state-specific behavior in separate objects and delegates behavior according to an object's current state.
- How it is used
- Models objects whose runtime behavior and allowed transitions depend on their current state.
- How deep it goes
- Explains centralized conditionals, state subclasses, polymorphic delegation, shared data, and returned transition objects.
- Examples
- Uses an automatic ticket machine with card validation, ticket purchase, invalid actions, and sold-out behavior.
- What you can do after
- Build it from scratch by separating state-specific actions into polymorphic classes and returning objects for state transitions.
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Software Design for Python Programmers
The State Design Pattern is a behavioral design pattern that allows an object to alter its behavior when its internal state changes by delegating state-specific behavior to separate state representations.
- How it is used
- Manages runtime states when an object's behavior and transitions depend critically on its current state.
- How deep it goes
- Explains the pattern through a conditional implementation, a polymorphic refactoring, a generic model, and a pattern comparison.
- Examples
- Uses an automatic ticket machine with READY, VALIDATING, TICKET_SOLD, and SOLD_OUT states.
- What you can do after
- Build it from scratch by separating state classes, delegating actions, and returning objects representing the next state.
Read how Software Design for Python Programmers explains state design pattern →
Related concepts
- design patternkind of · A design pattern is a reusable, general solution structure for a recurring software design problem in a particular context.
- state transitionuses · A state transition is a change from one modeled state of a system, object, or process to another according to an event, action, condition, or rule.
- stateuses · State is information or a configuration describing the condition of a system, entity, or computation at a particular time and potentially influencing subsequent behavior or decisions.
- behavioruses · Behavior is the externally observable actions, responses, outputs, or effects of a system or object under specified conditions or interactions.
- visitor design patterncontrasts with · The Visitor pattern separates operations on an object structure into visitor objects, allowing operations to be added without changing the structure’s element classes.
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