Program RefactoringProgram Refactoring

Mitch Soden

Union College

AgendaAgenda

• Definition– Unit Testing– Examples

• Why Refactor?

• Limitations

• Just Another SW Eng Practice?

• Automation tools

DefinitionDefinition

• Controlled/deliberate process

• Improve design/internal structure

• Existing code

• Behavior-preserving

Unit TestingUnit Testing

• Solid test suite - 1st step in refactoring

• Test after each refactoring

• Should be automated & self-checking

• Focus tests based on risk

Example – Extract MethodExample – Extract MethodMake 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 MethodExample – Extract MethodRefactored code:

...printBanner();

// perform calculationswhile (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 Example – Replace Error Code with Exceptionwith 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 Example – Replace Error Code with Exceptionwith Exception

Refactored code:

void withdraw(int amount) throws BalanceException {

if (amount > _balance) throw new BalanceException();

_balance -= amount;

}

Why Refactor?Why Refactor?

Problems

• Software modifications degrade structure

• Maintenance costs too high

• Inability to meet schedules

Why Refactor?Why Refactor?

Refactoring helps by

• Making software easier to understand

• Making software cheaper to modify

• Allowing developers become more productive

Limitations/DrawbacksLimitations/Drawbacks

• Time

• Human factor

• Changing interfaces

• Non-object oriented languages

Just Another Software Just Another Software Engineering Practice?Engineering Practice?

• Immediate payback

• Personal benefits

• It feels good

Automation ToolsAutomation Tools

Refactoring Browser– 1st refactoring tool built

– Univ. of Illinois PhD work

– Supports Smalltalk

– Integrates w/ Smalltalk Browser

Automation ToolsAutomation Tools

RefactorIt– Aqris Software, 2002

– Integrates w/ JBuilder, Forte, JDeveloper

– Many common refactorings

– Includes code metrics

– Automates auditing and corrective actions

Questions, comments, Questions, comments, opinions?opinions?