Packages

Packages :

1. Specification (required)
2. Body (optional)

(i)   Information hiding : Implementation is hidden in the package body.
(ii)  Public and private : Specification (public) & Body (private).
(iii) Initialization:  package is initialized only once per session.
(iv)  Session persistence : If we establish a session and execute a program that assigns a value to a package-level variable,
                            that variable is set to persist for the length of the session, and it retains its value even if the
                            program that performed the assignment has ended.

Example:

create or replace package test_package
as
my_variable1 number;
my_variable2 varchar2(200);
end;
/

Session 1:
Begin
  test_package.my_variable1:=1;
  test_package.my_variable2:='kiran';
End;
/

Begin
  dbms_output.put_line(test_package.my_variable1);
  dbms_output.put_line(test_package.my_variable2);
End;
/

Session 2:
Begin
  dbms_output.put_line(test_package.my_variable1);
  dbms_output.put_line(test_package.my_variable2);
End;
/

Note:
The first time our session uses a package (whether by calling a program defined in the package, reading or writing a variable, or using a locally declared variable TYPE), Oracle initializes that package.
A package may be reinitialized in a session if that package was recompiled since last use
or
if the package state for our entire session was reset.