This repository demonstrates all 23 Gang of Four (GoF) design patterns implemented in Java, modeled around real-world payment processing systems.
The examples are inspired by real-time banking and cross-border remittance platforms.
This repository models patterns within a payment technology ecosystem handling:
- IMPS – Instant domestic transfers
- NEFT – Batch-based low value settlement
- RTGS – High-value real-time gross settlement
- Cross-border remittance (SWIFT / correspondent banking)
- FX conversion and compliance workflows
- AML, KYC, sanctions screening
- Transaction lifecycle management
The goal is to demonstrate how classical design patterns apply to high-availability, fault-tolerant, and scalable financial systems.
Design patterns are grouped into three major categories:
Focus on object creation and lifecycle management.
Used in payment systems for:
- Payment processor instantiation
- Channel routing (IMPS/RTGS/SWIFT)
- Transaction request building
- Configuration management
Includes:
- Singleton
- Factory Method
- Abstract Factory
- Builder
- Prototype
Focus on class composition and system integration.
Used in payment systems for:
- SWIFT API integration
- Legacy core banking adapters
- Payment gateway facades
- Fraud check decorators
- Authorization proxies
Includes:
- Adapter
- Bridge
- Composite
- Decorator
- Facade
- Flyweight
- Proxy
Focus on object interaction and workflow orchestration.
Used in payment systems for:
- Validation pipelines (KYC → AML → Limits)
- Fee calculation strategies
- Transaction state transitions
- Event notifications
- Compliance auditing
Includes:
- Observer
- Strategy
- Command
- Chain of Responsibility
- State
- Template Method
- Iterator
- Mediator
- Memento
- Visitor
- Interpreter
Each pattern folder includes:
- Concept explanation
- Real-world payment use case
- Mermaid UML diagram
- Clean Java implementation
- Notes on scalability and production relevance
The repository reflects architectural challenges commonly found in:
- Distributed payment orchestration
- Idempotent transaction handling
- High-throughput real-time processing
- Resilient settlement workflows
- Event-driven notification systems
- Cross-border routing and FX abstraction
- Regulatory and compliance layering
Patterns are not presented in isolation — they are contextualized within payment domain challenges.
- Strengthen object-oriented and architectural thinking
- Apply SOLID principles in financial systems
- Model real-world payment workflows
- Demonstrate backend design maturity
- Serve as reference for senior backend & system design interviews
- Document reusable design solutions in payment platforms
As a backend engineer working in payment technology and cross-border remittance systems, this repository serves as:
- A knowledge base for reusable design solutions
- A domain-driven pattern reference
- A structured demonstration of production-level design thinking
- Combine multiple patterns into full payment orchestration flow
- Add event-driven architecture examples
- Add distributed system pattern integration
- Include concurrency and resilience patterns
- Model high-availability payment gateway architecture