Program Refactoring Mitch Soden Union College

Agenda Definition –Unit Testing –Examples Why Refactor? Limitations Just Another SW Eng Practice? Automation tools

Definition Controlled/deliberate process Improve design/internal structure Existing code Behavior-preserving

Unit Testing Solid test suite - 1 st step in refactoring Test after each refactoring Should be automated & self-checking Focus tests based on risk

Example – Extract Method Make code fragment into method whose name explains the purpose.... // print banner System.out.println (“*********************”); System.out.println (“*** Customer Info ***”); System.out.println (“*********************”); // perform calculations while (x.hasMoreElements()) {... } // print details System.out.println (“Name: ” + name); System.out.println (“Balance: ” + balance);

Example – Extract Method Refactored code:... printBanner(); // perform calculations while (x.hasMoreElements()) {... } printDetails(balance); } void printBanner() { System.out.println (“*********************”); System.out.println (“*** Customer Info ***”); System.out.println (“*********************”); } void printDetails(double balance) {...

Example – Replace Error Code with Exception Make a method throw an exception instead of returning a special code to indicate an error. int withdraw(int amount) { if (amount > _balance) return –1; else { _balance -= amount; return 0; }

Example – Replace Error Code with Exception Refactored code: void withdraw(int amount) throws BalanceException { if (amount > _balance) throw new BalanceException(); _balance -= amount; }

Why Refactor? Problems Software modifications degrade structure Maintenance costs too high Inability to meet schedules

Why Refactor? Refactoring helps by Making software easier to understand Making software cheaper to modify Allowing developers become more productive

Limitations/Drawbacks Time Human factor Changing interfaces Non-object oriented languages

Just Another Software Engineering Practice? Immediate payback Personal benefits It feels good

Automation Tools Refactoring Browser –1 st refactoring tool built –Univ. of Illinois PhD work –Supports Smalltalk –Integrates w/ Smalltalk Browser

Automation Tools RefactorIt –Aqris Software, 2002 –Integrates w/ JBuilder, Forte, JDeveloper –Many common refactorings –Includes code metrics –Automates auditing and corrective actions

Questions, comments, opinions?