Call package into a procedure, Oracle PL/SQL - oracle

Question

I'm trying to figure out this homework assignment we're supposed to solve in Oracle's 11g PL/SQL, but neither me nor my four friends have found a solution to this problem yet, and we're hoping someone more talented than us would give us a few pointers and/or comments about it.
Let's begin with the assignment in question (it's divided into two parts, and it's the last part we can't figure out):
First, create a procedure which fetches the current time with DBMS_UTILITY.GET_TIME, then performs a complex calculation. In the end, present how long it took (in seconds) to get the result/reach the answer.
And we've solved that one very well by creating a for-loop that calculates prime numbers (took roughly 5 seconds to calculate each prime number from 1 to 5000), however, the last part says this:
Now, create a package that will contain this complex calculation, and then re-write your procedure so that it calls in the "package method" of that calculation. Your procedure will now just measure the starting-time, call in the package with the calculation, and present how long it took (in seconds) to get the result/reach the answer.
So, to recap: the procedure will measure the time it takes for the package to make the calculation. And this is where we're stuck. There's not much information on the net about this, but my code looks like this:
SET SERVEROUTPUT ON
CREATE OR REPLACE PROCEDURE time_measure_procedure
AS
time_start NUMBER;
time_end NUMBER;
time_diff NUMBER;
BEGIN
time_start := dbms_utility.get_time;
--This is where I'd presumably call in the
--package into the procedure, whereas the time
--will be measured until the calculation is done.
heavy_calculation_package;
time_end := dbms_utility.get_time;
time_diff := ( time_end - time_start ) / 100;
dbms_output.Put_line('Time it took: ' || time_diff || ' seconds.');
END time_measure_procedure;
/
CREATE OR REPLACE PACKAGE BODY heavy_calculation_package
AS
PROCEDURE time_measure_procedure
IS
x NUMBER;
counter NUMBER;
BEGIN
--This is the prime number calculation, which
--we're supposed to call into the procedure.
FOR n IN 1 .. 5000 LOOP
counter := 0;
x := Floor(n / 2);
FOR i IN 2 .. x LOOP
IF ( MOD(n, i) = 0 ) THEN
counter := 1;
END IF;
END LOOP;
IF ( counter = 0 ) THEN
dbms_output.Put_line(n ||' is a prime number.');
END IF;
END LOOP;
END time_measure_procedure;
END heavy_calculation_package;
/
The errors I receive are typically:
object package_heavy_calc is invalid
cannot compile body of package_heavy_calc without its specification
Does anyone have any clue to why this isn't working? Any hints or pointers at all would be lovely!

Answer 1

You need to have a package in a valid state before you can call it. In this case you need to declare the package first like this:
CREATE OR REPLACE PACKAGE package_heavy_calc
AS
PROCEDURE heavy_calc;
END PACKAGE_HEAVY_CALC;
You can have a package without a body but not a body without a package. You could do this by putting the code in the package head. For your purposes declare the package and the package body, much easier.
As an aside naming is critical for good readable code. I would have named your package PKG_MATH and the procedure P_CALC_PRIME_NUMBERS so when you call it you have an idea of what it does. Naming however is like sport's teams, everyone has a favorite one and the style can be quite different.

Answer 2

Please add the package specs and then try. Below is a snippet which
will help you.
CREATE OR REPLACE PACKAGE package_heavy_calculation
AS
PROCEDURE heavy_calc;
END package_heavy_calculation;
CREATE OR REPLACE PACKAGE BODY package_heavy_calculation
AS
PROCEDURE heavy_calc
IS
x NUMBER;
counter NUMBER;
BEGIN
--This is the prime number calculation, which
--we're supposed to call into the procedure.
FOR n IN 1 .. 5000
LOOP
counter := 0;
x := Floor(n / 2);
FOR i IN 2 .. x
LOOP
IF ( MOD(n, i) = 0 ) THEN
counter := 1;
END IF;
END LOOP;
IF ( counter = 0 ) THEN
dbms_output.Put_line(n ||' is a prime number.');
END IF;
END LOOP;
END heavy_calc;
END package_heavy_calculation;