What is the difference between abstract class and interface?

Question

Accepted Answer

**Abstract class** — can have implementation. **Interface** — only contract.

```csharp
// Abstract class
public abstract class Animal {
    public string Name { get; set; }

// Can have implementation
    public void Eat() {
        Console.WriteLine("Eating...");
    }

// Must be implemented
    public abstract void MakeSound();
}

// Interface
public interface IAnimal {
    string Name { get; set; }
    void MakeSound();
}
```

- Abstract class — single inheritance.
- Interface — multiple inheritance.
- Abstract class — can have fields.
- Interface — no fields (until C# 8).

C#: What is the difference between abstract class and interface?