In Part 1 of this series, we talked about how Oracle objects compare to Java and how to create Oracle Objects. In Part 2, I covered we covered object comparison and type inheritance. Today, we’ll talk about polymorphism and type evolution.

Like parts 1 and 2, this will be a technical discussion.

Polymorphism

First a definition. What is Polymorphism and why is it important? One of the best definitions I have found is this link at OnJava. You can skip the part about object serialization. Not really that important to Oracle’s OO as you’re already in the database.

Let’s go back to our (most basic) calculator example.

CREATE OR REPLACE TYPE Calculator AS OBJECT (
  value NUMBER,
  MEMBER PROCEDURE print,
  MEMBER PROCEDURE add1( p_amt IN NUMBER ),
  MEMBER PROCEDURE subtract( p_amt IN NUMBER )
  )
  NOT FINAL;
/

CREATE OR REPLACE TYPE BODY Calculator AS
  MEMBER PROCEDURE print IS
  BEGIN
    DBMS_OUTPUT.PUT_LINE( TO_CHAR( value ) );
  END;

  MEMBER PROCEDURE add1( p_amt IN NUMBER )  IS
  BEGIN
    value := value + p_amt;
  END;

  MEMBER PROCEDURE subtract( p_amt IN NUMBER )  IS
  BEGIN
    value := value - p_amt;
  END;

END;
/

And our Advanced Calculator:

CREATE OR REPLACE TYPE AdvancedCalculator UNDER Calculator (
  pi FLOAT,
  CONSTRUCTOR FUNCTION AdvancedCalculator
     RETURN SELF AS RESULT ,
  MEMBER PROCEDURE multiply( p_amt IN NUMBER ),
  MEMBER PROCEDURE divide( p_amt IN NUMBER ),
  OVERRIDING MEMBER PROCEDURE print
   )
NOT FINAL;
/

This isn’t exactly the same AdvancedCalculator.

It looks like the job market for Oracle is opening up. I’m seeing many of my friends find new jobs and I’m doing a lot of interviewing at work. I hope this is a trend that continues. In this entry, I share my method for interviewing Oracle resources and provide some sample interview questions and answers for developers.

Interviewing anyone can be difficult. Interviewing technical resources is very difficult. To me, probably the hardest thing is pinpointing exactly what you want this person to do. What, exactly, will this person be doing in their day-to-day job?

I ran across this link while looking for something else. This is a discussion about Oracle PowerBrowser. Talk about a ride in the way back machine!

Lewis

Technorati : backmachine, browser, html, internet, nostalgia, oracle, oraclepowerbrowser

I’m going to start a new daily entry in addition to my other entries. I’ll call it the Thought of the Day. It will be an interesting link or thought or joke or just something I read somewhere. It will usually pertain, somehow, to Oracle but like today it might not.

Today’s thought is a link to the best Bash Shell Script guide I’ve ever seen. It’s a reference and a tutorial. I’m no Linux guru and certainly no scritping guru but I really like this guide.

Advanced Bash-Scripting Guide

Thanks,

Lewis