are processed at compile time, not at run time.
In PL/SQL, the pragma EXCEPTION_INIT tells the compiler to associate an exception name with an Oracle error number. That allows you to refer to any internal exception by name and to write a specific handler for it. You code the pragma EXCEPTION_INIT in the declarative part of a PL/SQL block, subprogram, or package using the syntax
PRAGMA EXCEPTION_INIT(exception_name, Oracle_error_number);
where exception_name is the name of a previously declared exception. The pragma must appear somewhere after the exception declaration in the same declarative section, as shown in the following example: