What method cannot be overridden in object-oriented programming?

In object-oriented programming, there is a concept known as "final" or "non-overridable" methods. These are methods that are declared in such a way that child classes cannot modify their implementation.

Depending on the programming language, the syntax for declaring such methods may differ:

• Java: Uses the keyword final.

  public final void cannotOverride() {
      // This method cannot be overridden in child classes
  }
  

• C#: Uses the keyword sealed.

  public sealed override void CannotOverride() {
      // This method overrides a base class method and is now sealed
  }
  
  // Or make the method sealed from the start if it is not overridden
  public sealed void CannotOverrideFromStart() {
      // This method cannot be overridden
  }
  

• Python: Does not have a built-in mechanism to prevent method overriding at the syntax level. This is usually achieved through convention or using decorators / metaclasses, although they do not provide absolute guarantees.

Thus, a method marked as final (Java) or sealed (C#) is a method that cannot be overridden in child classes.