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LLDsystem_design~12 mins

State pattern in LLD - Architecture Diagram

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System Overview - State pattern

The State pattern helps a system change its behavior when its internal state changes. It allows an object to appear to change its class by switching between different state objects. This is useful for managing complex state-dependent logic in a clean and scalable way.

Architecture Diagram
  +---------+        +-------------+        +-------------+
  | Context | -----> | State A     | <----> | State B     |
  +---------+        +-------------+        +-------------+
       |                    |                      |
       |                    |                      |
       +--------------------+----------------------+
                            |
                      +-------------+
                      | State C     |
                      +-------------+
Components
Context
object
Maintains a reference to a State object that defines the current state.
State A
state
Represents one possible state with its own behavior.
State B
state
Represents another possible state with different behavior.
State C
state
Represents a third possible state with its own behavior.
Request Flow - 4 Hops
User → Context
Context → Current State (e.g., State A)
Current State → Context
Context → User
Failure Scenario
Component Fails:State object
Impact:If a State object has a bug or is missing, the Context may behave incorrectly or throw errors during state transitions or actions.
Mitigation:Use thorough testing of each State implementation and ensure Context validates state transitions. Use default or fallback states to handle unexpected conditions.
Architecture Quiz - 3 Questions
Test your understanding
What role does the Context object play in the State pattern?
AIt defines all possible states and their behaviors.
BIt holds the current state and delegates actions to it.
CIt directly implements all state behaviors.
DIt manages user input and output only.
Design Principle
The State pattern encapsulates state-specific behavior into separate objects, allowing the Context to change its behavior dynamically by switching states. This promotes cleaner code, easier maintenance, and better scalability for systems with complex state-dependent logic.