Don't repeat yourself

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
  }
}

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
  }
}

Resources:

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

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