Adapter pattern in LLD - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Purpose of the Adapter Pattern

Which of the following best describes the main purpose of the Adapter pattern in system design?

A To allow incompatible interfaces to work together by converting one interface into another expected by clients.

B To provide a way to access elements of a collection sequentially.

C To enforce strict type checking at compile time.

D To create multiple instances of a class to improve performance.

💡 Hint

Think about how two parts of a system with different interfaces can communicate.

The Adapter pattern acts as a bridge between two incompatible interfaces, allowing them to work together without changing their existing code.

❓ Architecture

intermediate

Identifying Adapter Pattern Components

In the Adapter pattern, which component is responsible for implementing the target interface and holding a reference to the adaptee?

A Adaptee

B Adapter

C Client

D Target

💡 Hint

This component acts as a bridge between the client and adaptee.

The Adapter implements the target interface and holds a reference to the adaptee, translating calls from the client to the adaptee.

❓ scaling

advanced

Scaling Adapter Pattern in Large Systems

When scaling a system that uses multiple adapters for different incompatible interfaces, which approach best maintains system scalability and manageability?

A Use a registry or factory to manage and provide specific adapters dynamically based on client requests.

B Create a single monolithic adapter that handles all interface conversions.

C Hardcode adapter selection logic inside the client code for each interface type.

D Duplicate adapter code for each client to reduce dependencies.

💡 Hint

Think about how to avoid tight coupling and improve flexibility when many adapters exist.

Using a registry or factory pattern to manage adapters allows dynamic selection and easier maintenance, improving scalability.

❓ tradeoff

advanced

Tradeoffs of Using Adapter Pattern

What is a common tradeoff when applying the Adapter pattern in system design?

A It always improves performance by reducing method calls.

B It reduces code readability by merging unrelated functionalities into one class.

C It eliminates the need for interfaces, simplifying the design.

D It increases system complexity by adding extra layers but improves flexibility and reusability.

💡 Hint

Consider what happens when you add an extra component between client and adaptee.

Adapters add an extra layer which can increase complexity but allow incompatible interfaces to work together, enhancing flexibility.

❓ component

expert

Request Flow in Adapter Pattern

Consider a client calling a method on a target interface implemented by an adapter, which internally calls the adaptee's method. What is the correct sequence of method calls in this flow?

A 2,1,3,4

B 1,3,2,4

C 1,2,3,4

D 1,2,4,3

💡 Hint

Follow the call from client to adaptee step-by-step.

The client calls the target interface method, the adapter translates and forwards the call to the adaptee, which executes and returns the result.

Practice

1. What is the main purpose of the Adapter pattern in system design?

easy

A. To improve the performance of a system by caching results

B. To allow incompatible interfaces to work together by converting one interface to another

C. To store data persistently in a database

D. To create multiple instances of a class

Solution

1. Step 1: Understand the Adapter pattern role

   The Adapter pattern acts as a bridge between two incompatible interfaces, allowing them to communicate.

2. Step 2: Compare with other options

   The other options describe different design goals unrelated to interface compatibility.

3. Final Answer:

   To allow incompatible interfaces to work together by converting one interface to another -> Option B

4. Quick Check:

   Adapter pattern = interface compatibility [OK]

Hint: Adapter = bridge between incompatible interfaces [OK]

Common Mistakes:

• Confusing Adapter with Singleton or Factory patterns
• Thinking Adapter improves performance directly
• Assuming Adapter stores data

2. Which of the following is the correct way to declare an Adapter class in a typical object-oriented language?

easy

A. class Adapter implements Adaptee { private TargetInterface target; }

B. class Adapter extends Adaptee implements TargetInterface { }

C. class Adapter extends TargetInterface { private Adaptee adaptee; }

D. class Adapter implements TargetInterface { private Adaptee adaptee; }

Solution

1. Step 1: Identify Adapter pattern structure

   The Adapter class implements the TargetInterface and holds a reference to the Adaptee to delegate calls.

2. Step 2: Analyze options

   class Adapter implements TargetInterface { private Adaptee adaptee; } correctly shows Adapter implementing TargetInterface and containing Adaptee. The other options misuse inheritance or interfaces.

3. Final Answer:

   class Adapter implements TargetInterface { private Adaptee adaptee; } -> Option D

4. Quick Check:

   Adapter implements target and wraps adaptee [OK]

Hint: Adapter implements target interface, holds adaptee instance [OK]

Common Mistakes:

• Using inheritance incorrectly instead of composition
• Confusing which interface to implement
• Swapping adaptee and target roles

3. Given this Adapter pattern code snippet, what will be the output?

class Adaptee {
  String specificRequest() { return "Adaptee response"; }
}

interface Target {
  String request();
}

class Adapter implements Target {
  private Adaptee adaptee = new Adaptee();
  public String request() {
    return adaptee.specificRequest();
  }
}

public class Main {
  public static void main(String[] args) {
    Target target = new Adapter();
    System.out.println(target.request());
  }
}

medium

A. Adaptee response

B. Target response

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Trace method calls in Adapter

   The Adapter's request() calls adaptee.specificRequest(), which returns "Adaptee response".

2. Step 2: Check main method output

   Main creates Adapter as Target and prints target.request(), so output is "Adaptee response".

3. Final Answer:

   Adaptee response -> Option A

4. Quick Check:

   Adapter delegates request() to adaptee.specificRequest() [OK]

Hint: Adapter.request() returns adaptee.specificRequest() result [OK]

Common Mistakes:

• Expecting 'Target response' instead of adaptee's
• Assuming compilation or runtime errors without cause
• Confusing method names

4. Identify the error in this Adapter pattern implementation:

interface Target {
  void request();
}

class Adaptee {
  void specificRequest() { System.out.println("Adaptee called"); }
}

class Adapter implements Target {
  Adaptee adaptee = new Adaptee();
  public void request() {
    specificRequest();
  }
}

medium

A. Adapter calls specificRequest() without referencing adaptee instance

B. Adaptee should implement Target interface

C. Adapter should extend Adaptee instead of implementing Target

D. Target interface method signature is incorrect

Solution

1. Step 1: Review Adapter's request() method

   Adapter calls specificRequest() directly, but specificRequest() belongs to Adaptee instance, so it should call adaptee.specificRequest().

2. Step 2: Validate other options

   Adaptee does not need to implement Target. Adapter implements Target correctly. Target interface method is correct.

3. Final Answer:

   Adapter calls specificRequest() without referencing adaptee instance -> Option A

4. Quick Check:

   Adapter must call adaptee.specificRequest() [OK]

Hint: Call adaptee methods via adaptee instance inside Adapter [OK]

Common Mistakes:

• Calling adaptee methods without instance prefix
• Misusing inheritance instead of composition
• Changing Target interface unnecessarily

5. You need to integrate a legacy payment system with a new e-commerce platform. The legacy system has a method processLegacyPayment(), but the platform expects processPayment(). How should you apply the Adapter pattern to solve this?

hard

A. Create a new payment system and discard the legacy system

B. Modify the legacy system to rename processLegacyPayment() to processPayment()

C. Create an Adapter class implementing the platform's payment interface and inside it call processLegacyPayment() of the legacy system

D. Use inheritance to make the legacy system extend the platform's payment interface

Solution

1. Step 1: Understand integration requirement

   The platform expects processPayment(), but legacy system only has processLegacyPayment().

2. Step 2: Apply Adapter pattern

   Create an Adapter that implements the platform interface and inside calls legacy's processLegacyPayment() to adapt calls without changing legacy code.

3. Step 3: Evaluate other options

   Modifying the legacy code is risky. Discarding the legacy system is costly. Using inheritance is not possible if the legacy system is not designed for it.

4. Final Answer:

   Create an Adapter class implementing the platform's payment interface and inside it call processLegacyPayment() of the legacy system -> Option C

5. Quick Check:

   Adapter wraps legacy method to match platform interface [OK]

Hint: Adapter wraps legacy calls to match new interface [OK]

Common Mistakes:

• Changing legacy code directly
• Ignoring Adapter pattern benefits
• Trying inheritance when not supported