An override method provides a new implementation of a member inherited from a base class. The method overridden by an override declaration is known as the overridden base method. The overridden base method must have the same signature as the override method. For information on inheritance, see Inheritance.
You cannot override a non-virtual or static method. The overridden base method must be virtual, abstract, or override.
An override declaration cannot change the accessibility of the virtual method. Both the override method and the virtual method must have the same access level modifier.
You cannot use the modifiers new, static, virtual, or abstract to modify an override method.
An overriding property declaration must specify the exact same access modifier, type, and name as the inherited property, and the overridden property must be virtual, abstract, or override.