You are only allowed to define a property accessor method for a property if
- the class in which the method is defined also defines the property
- the class does not include a properties block that defines that property but does allow dynamic properties (see the Set and Get Methods for Dynamic Properties documentation page linked in the See Also section), or
- the property is Abstract in its defining class, in which case a concrete subclass can define a property accessor method
No, a superclass defining a property in its properties block does not allow its subclasses to define a property accessor method. Doing so could allow the subclass to accept a value that would make the subclass instance not a valid superclass instance.
Consider a hierarchy where EquilateralTriangle inherits from Triangle. Triangle defines a property numSides and validates that this property always has value 3. [Yes, it should be a Constant property and not have a property accessor method, but this is a simplified example to illustrate a point.] If EquilateralTriangle could define a property accessor method that allows numSides to be 4 (due to a bug in the method) and you created an EquilateralTriangle with numSides equal to 4, it would not be a valid Triangle.