From Oracle 12c documentation:
You can overload user-defined constructors, like other type methods.
User-defined constructors are not inherited, so a user-defined constructor defined in a supertype cannot be hidden in a subtype. However, a user-defined constructor does hide, and thus supersede, the attribute-value constructor for its type if the signature of the user-defined constructor exactly matches the signature of the attribute-value constructor. For the signatures to match, the names and types of the parameters (after the implicit SELF parameter) of the user-defined constructor must be the same as the names and types of the attributes of the type. The mode of the parameters (after the implicit SELF parameter) of the user-defined constructor must be IN.
If an attribute-value constructor is not hidden by a user-defined constructor that has the same name and signature, the attribute-value constructor can still be called.
Note that, if you evolve a type—for example, by adding an attribute—the signature of the attribute-value constructor of the type changes accordingly. This can cause a formerly hidden attribute-value constructor to become usable again.