how to check programatically wether a oracle stored procedure has default valued parameters?

I want to get the collection OracleParameter[] of all the stored
procedure parameters which are assigned default values in stored proc.
The way in which I was trying out was to get the parameter array with
the help of OracleCommandBuilder.DeriveParameter() method. But this
method only gives the name,datatype,size,isnullable properties of the
parameter.This method does not gives any property to check if the
parameter has default value or not.

So issues are;-
1> How to check if the parameter has default value or not?
2> How to get that default value?

thanx

.