Don't repeat yourself

The code says everything once and only once, which is the essence of good design. -- Martin Fowler

[Time: 4:44 mins]

• Repititive code makes maintainance more difficult
• There are more places to change
• We may forget to change some of them
• Increases probability of bugs
• Types of repitition
• In methods in a class
• Accross the entire software 

Example 1: DRY violated

public class Account {   public void transferFunds(double amt, Account dest) {     //transfer funds     //generate email... create connection     //create message     //dispatch email   }   public void delete() {     //delete account     //generate email... create connection     //create message     //dispatch email   } }

Java2html

Example 2: DRY honoured

public class Account {   public void transferFunds(double amt, Account dest) {     //transfer funds     dispatchEmail(...);   }   public void delete() {     //delete account     dispatchEmail(...);   }   public dispatchEmail() {     //generate email... create connection     //create message     //dispatch email   } }

Java2html

Resources:

• http://www.artima.com/intv/dry.html
• http://c2.com/cgi/wiki?DontRepeatYourself
• http://c2.com/cgi/wiki?OnceAndOnlyOnce
  

Note: This post was originally posted on my blog at http://www.adaptivelearningonline.net