What is an Interface? When is it used?

Difficulty: 5/10

polymorphism, dependency injection, contract design

Interface

An interface defines a contract that implementing types agree to satisfy. It focuses primarily on what an object can do rather than how it stores or implements that behavior. Interfaces are valuable for loose coupling, dependency injection, multiple capabilities, testability and substituting implementations. For example, an application can depend on a PaymentGateway interface while different implementations support Stripe, Razorpay, a bank gateway or a test fake.

javascript

1
Defines a contract or capability.
2
Reduces dependency on concrete implementations.
3
Supports multiple implementations.
4
Works naturally with dependency injection.
5
Improves unit testing by allowing test doubles.
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The exact capabilities of interfaces vary between languages.

Scenario Questions

0-2 years experience

2-5 years experience

1A new class was added that implements an existing Logger interface, but after deployment some log messages are missing. Walk me through how you'd investigate the issue.

What is an Interface? When is it used?

Interface

Scenario Questions

Follow-up Questions