Duplicate code smell

Duplicated code is the smelliest of the code smells. The book Refactoring Martin Fowler 1999 states that: "If you see the same code structure in more than one place, you can be sure that your program will be better if you find a way to unify them." Martin Fowler 1999 states that the simplest duplicated code problem is when you have the same expression in two methods of the same class.

Refactoring

The best way to fix this bad code smell is to use Extract Method as shown below.

       printOwing() {
               printBanner();
       
               //print details
               System.out.println ("name:	" + _name);
               System.out.println ("amount	" + getOutstanding());
       }

becomes

       void printOwing() {
               printBanner();
               printDetails(getOutstanding());
       }

       void printDetails (double outstanding) {
               System.out.println ("name:	" + _name);
               System.out.println ("amount	" + outstanding);
       }

See also

• Don't repeat yourself
• Once and only once
• Code smells
• Refactoring