Program to interface not implementation in LLD - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does 'Program to interface, not implementation' mean in system design?

It means writing code that depends on abstract interfaces rather than concrete classes. This allows flexibility to change implementations without affecting the rest of the system.

intermediate

Why is programming to an interface beneficial for scalability?

Because it allows swapping or adding new implementations without changing the code that uses the interface, making the system easier to extend and scale.

beginner

Give a real-life analogy for 'Program to interface, not implementation'.

Like using a TV remote control (interface) without caring about the brand or model (implementation). You just press buttons and expect it to work.

intermediate

How does programming to interface improve testing?

It allows using mock or fake implementations of interfaces during testing, making tests isolated and easier to write.

advanced

What is a common design pattern that supports programming to interface?

The Dependency Injection pattern, which injects implementations of interfaces into classes, promoting loose coupling.

What is the main advantage of programming to an interface?

A Allows changing implementations without affecting dependent code

B Makes code run faster

C Reduces the number of lines of code

D Eliminates the need for testing

Programming to an interface allows changing the underlying implementation without changing the code that uses it.

Which of these best describes an interface in programming?

A A contract defining methods without implementation

B A detailed class with full implementation

C A database schema

D A user interface design

An interface defines method signatures without implementation, acting as a contract.

How does programming to interface help in testing?

A By removing the need for tests

B By making tests run automatically

C By allowing use of mock implementations

D By making code shorter

Mock implementations of interfaces can be used to isolate tests from real dependencies.

Which design pattern is closely related to programming to interface?

A Singleton

B Factory

C Observer

D Dependency Injection

Dependency Injection provides implementations of interfaces to classes, supporting loose coupling.

What happens if you program directly to implementation instead of interface?

A Code becomes more flexible

B Code becomes tightly coupled and harder to change

C Code runs faster

D Code requires no documentation

Programming to implementation creates tight coupling, making changes difficult.

Explain the concept of 'Program to interface, not implementation' with a simple example.

Think about how using a remote control hides the TV details.

Describe how programming to interface improves system flexibility and testing.

Consider how changing parts without breaking others helps.