SOLID & Design Patterns Interview Question #26

What is the Adapter Pattern?

Structural, Creational & Behavioral Patterns Junior Beginner

Quick Interview Answer

The Adapter Pattern converts the interface of an existing class into an interface that a client expects. It is useful when an application must integrate a legacy component, third-party library, or external service whose API does not match the application's abstraction.

Detailed Explanation

The adapter contains the translation logic so the rest of the application does not depend directly on the incompatible API. This reduces coupling to external implementation details.

Code Example

public interface IPaymentGateway
{
    Task PayAsync(decimal amount);
}

public class LegacyGatewayAdapter : IPaymentGateway
{
    private readonly LegacyGateway _legacy;

    public LegacyGatewayAdapter(LegacyGateway legacy)
        => _legacy = legacy;

    public Task PayAsync(decimal amount)
    {
        _legacy.MakePayment((double)amount);
        return Task.CompletedTask;
    }
}