C# Interfaces

Contracts that classes implement.

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An interface declares members that implementing classes must provide. By convention, interface names start with I.

class Card : IPayment
A class can implement many interfaces.
Interfaces enable loose coupling and are central to dependency injection in ASP.NET Core.

Key Takeaways: C# Interfaces

Mastering C# Interfaces helps you write clean and reliable C# code. Follow standard conventions, test edge cases, and keep logic simple. Try running the code example below and complete the exercises to build confidence.

C# Interfaces Code Example

IPayment[] methods = { new Card(), new JazzCash() };
decimal amount = 10000m;

foreach (var m in methods)
{
    Console.WriteLine($"{m.Name}: fee {m.Fee(amount)}");
}

interface IPayment
{
    string Name { get; }
    decimal Fee(decimal amount);
}

class Card : IPayment
{
    public string Name => "Card";
    public decimal Fee(decimal amount) => amount * 0.025m;
}

class JazzCash : IPayment
{
    public string Name => "JazzCash";
    public decimal Fee(decimal amount) => 20m;
}

Output