Strategy pattern in LLD - Architecture Diagram

System Overview - Strategy pattern

The Strategy pattern allows a system to select an algorithm's behavior at runtime. It defines a family of algorithms, encapsulates each one, and makes them interchangeable. This helps in changing the algorithm independently from clients that use it.

Architecture Diagram

User
  |
  v
Context
  |
  v
+-----------------+
|  Strategy (interface)  |
+-----------------+
   /       |       \
  /        |        \
ConcreteStrategyA ConcreteStrategyB ConcreteStrategyC
  |          |          |
  v          v          v
AlgorithmA AlgorithmB AlgorithmC

Components

User

actor

Initiates requests to the Context to perform an operation.

Context

service

Maintains a reference to a Strategy object and delegates algorithm execution to it.

Strategy (interface)

interface

Defines a common interface for all supported algorithms.

ConcreteStrategyA

service

Implements the algorithm using Strategy A.

ConcreteStrategyB

service

Implements the algorithm using Strategy B.

ConcreteStrategyC

service

Implements the algorithm using Strategy C.

Request Flow - 5 Hops

User → Context

Context → Strategy (interface)

Strategy (interface) → ConcreteStrategyA/B/C

ConcreteStrategyA/B/C → Context

Context → User

Failure Scenario

Component Fails:ConcreteStrategyA/B/C

Impact:If the selected Concrete Strategy fails, the operation cannot complete correctly and may cause errors or incorrect results.

Mitigation:Context can catch errors and fallback to a default or alternative Concrete Strategy to maintain system stability.

Architecture Quiz - 3 Questions

Which component decides which algorithm to use at runtime?

A User

B ConcreteStrategy

C Context

D Strategy interface

Design Principle

The Strategy pattern separates algorithm selection from implementation, allowing flexible swapping of algorithms at runtime without changing the client code. This promotes open/closed principle and easier maintenance.