Separated Interface Design Pattern

Master Software Architecture & Design Patterns!

Subscribe to Ram N Java for beginner-friendly, practical software engineering guides!

🔔 Subscribe to Our Channel

What is the Separated Interface Pattern?

The Separated Interface pattern belongs to the base patterns family in enterprise application architecture. In simple terms, it is an architectural approach where you define an interface in one package or module and put its implementation in another separate package.

In standard object-oriented design, you often want a client module or domain layer to use a service without depending directly on the package where that service is implemented. Separating the interface breaks unwanted compile-time coupling and dependency cycles between packages.

How Does it Work? (Package Structure)

The core mechanism revolves around package boundaries:

• Client / Domain Package: Contains the domain logic (e.g., OrderProcessor or CustomerService) along with the Interface definition (e.g., BillingGateway). The domain code only talks to this interface.
• Implementation Package: Lives in a separate package or JAR (e.g., PayPalBillingService or StripeBillingService) and implements the interface defined in the domain package.
• Inversion of Control: The implementation package depends on the domain package (where the interface resides), but the domain package has zero compile-time dependency on the implementation package.

Key Advantages

• Decoupled Compilation: Changes or updates to the implementation package never force recompilation of the client/domain package.
• Easy Mocking & Unit Testing: Unit tests can run isolated against lightweight mocks or stubs of the interface without pulling in heavy implementation dependencies.
• Pluggable Implementations: You can easily swap out or add alternative implementations (such as different third-party providers or database drivers) at runtime or configuration time without affecting business rules.

Watch Related Architecture Tutorials:

• 👉 Plugin Design Pattern Explained
• 👉 Gateway Design Pattern Explained
• 👉 Base Design Pattern: A Comprehensive Overview

---

Click here to watch in Youtube : https://www.youtube.com/watch?v=d3k-hOA7k2Y

Click the below Image to Enlarge

Separated Interface Design Pattern

See also:

All Design Patterns Links