Adapter pattern in LLD - System Design Exercise

Design: Adapter Pattern Implementation

Design and implement the adapter pattern to connect incompatible interfaces in a low-level design context. Out of scope are other design patterns or large system integrations.

Functional Requirements

FR1: Allow two incompatible interfaces to work together without changing their existing code

FR2: Enable reuse of existing classes with different interfaces

FR3: Support multiple types of adapters for different incompatible interfaces

FR4: Ensure the adapter is transparent to the client using the target interface

Non-Functional Requirements

NFR1: The adapter should not modify the existing adaptee or target interfaces

NFR2: The solution should be simple and maintainable

NFR3: Adapters should be easy to add or remove without affecting other parts of the system

NFR4: Performance overhead introduced by the adapter should be minimal

Think Before You Design

Questions to Ask

❓ Question 1

❓ Question 2

❓ Question 3

❓ Question 4

❓ Question 5

Key Components

Target interface expected by the client

Adaptee interface that is incompatible

Adapter class that implements the target interface and holds a reference to the adaptee

Client code that uses the target interface

Design Patterns

Adapter pattern (object adapter and class adapter variants)

Facade pattern for simplifying complex interfaces

Decorator pattern if additional behavior is needed

Proxy pattern if controlling access is required

Reference Architecture

Client --> Target Interface --> Adapter --> Adaptee

Where:
- Client calls methods on Target Interface
- Adapter implements Target Interface and translates calls to Adaptee
- Adaptee has incompatible interface but provides needed functionality

Components

Target Interface

Interface or Abstract Class

Defines the interface expected by the client

Adaptee

Existing Class with incompatible interface

Provides the actual functionality but with a different interface

Adapter

Class implementing Target Interface

Converts calls from Target Interface to Adaptee's interface

Client

Any

Uses the Target Interface without knowing about the Adaptee

Request Flow

1. Client calls a method on the Target Interface

2. Adapter receives the call and translates it to the Adaptee's method call

3. Adapter calls the corresponding method on the Adaptee

4. Adaptee executes the method and returns the result to the Adapter

5. Adapter returns the result back to the Client

Database Schema

Not applicable for this design pattern as it focuses on interface compatibility and object structure.

Scaling Discussion

Bottlenecks

Multiple adapters increase code complexity and maintenance overhead

Performance overhead if adapters add significant translation logic

Difficulty managing many adapters if interfaces change frequently

Solutions

Use automated tools or code generation to create adapters when possible

Keep adapter logic simple and focused on translation only

Use interface segregation to minimize the number of methods adapters must implement

Document adapters clearly and group related adapters for easier maintenance

Interview Tips

Time: Spend 10 minutes explaining the problem and requirements, 15 minutes designing the adapter pattern with diagrams and code examples, and 5 minutes discussing scaling and trade-offs.

Explain the problem of incompatible interfaces and why adapter pattern is useful

Describe the difference between object adapter and class adapter

Show how the adapter translates calls between client and adaptee

Discuss how this pattern promotes code reuse and flexibility

Mention potential performance impacts and maintenance considerations