Sealed classes

Context: The sealed modifier prevents other classes from inheriting from a class. It also prevents overriding of methods (when applied to a method).

Sealed Class

public sealed class FinalClass
{
    // cannot be derived from
}
// public class Derived : FinalClass { } // error

Sealed Method

A sealed method overrides a virtual method but cannot be overridden further.

public class Parent
{
    public virtual void Method() { }
}
public class Child : Parent
{
    public sealed override void Method() { }
}
public class GrandChild : Child
{
    // public override void Method() { } // error: sealed
}

Use Cases

• Prevent unintended inheritance (security, design).
• Improve performance (virtual dispatch can be optimized).
• Immutability (e.g., string is sealed).