Iterator pattern in LLD - Architecture Diagram

System Overview - Iterator pattern

The Iterator pattern provides a way to access elements of a collection sequentially without exposing its underlying representation. It allows clients to traverse different types of collections uniformly and safely.

Key requirements include supporting multiple collection types and enabling traversal without modifying the collection.

Architecture Diagram

User
  |
  v
Iterator Interface <---- Collection Interface
  |                      |
  v                      v
Concrete Iterator     Concrete Collection
  |                      |
  +----------------------+

Components

User

client

Requests to traverse elements in a collection

Iterator Interface

interface

Defines methods to traverse elements (e.g., next(), hasNext())

Concrete Iterator

service

Implements traversal logic for a specific collection

Collection Interface

interface

Defines method to create an iterator

Concrete Collection

service

Implements collection storage and returns its iterator

Request Flow - 6 Hops

User → Concrete Collection

Concrete Collection → Concrete Iterator

User → Concrete Iterator

Concrete Iterator → Concrete Collection

Concrete Iterator → User

User → Concrete Iterator

Failure Scenario

Component Fails:Concrete Iterator

Impact:Traversal stops or returns incorrect elements; user cannot access collection elements properly

Mitigation:Implement robust iterator logic with boundary checks; fallback to safe defaults or error handling to prevent crashes

Architecture Quiz - 3 Questions

Which component is responsible for defining the traversal methods like next() and hasNext()?

A Concrete Collection

B User

C Iterator Interface

D Concrete Iterator

Design Principle

The Iterator pattern separates traversal logic from collection storage, enabling uniform access to elements without exposing internal structure. This promotes flexibility and encapsulation.