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ECE 750 Topic 8

Meta-programming languages, systems, and applications

Evolving Object-Oriented Designs with Refactorings – Lance Tokuda and Don Batory

July 29, 2004

Presented by Shimin Li

ECE750 University of waterloo

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Paper Overview

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Contents: Overview

Roughly five parts:

• Introduction• Overview of Refactorings• Examples of Evolving Applications• Lessons Learned from experiments• Related work and Conclusion

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Contents: Detail

• Introductio– Automate design level changes of source code– Preserve behavior

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Contents: Detail

• Overview of Refactorings– Definition of refactoring– Enabling conditions for refactorings

• Ensure refactorings preserve behavior

– Classification of object-oriented refactorings• Schema refactorings• Pattern refectorings• Language-specific refactorings

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Contents: Detail

• Examples of Evolving Applications– Why these examples have been chosen– Evolving CIM Works

• Version 2 to version 4• Nine steps, 81 refactorings, 486 lines of code modified

– Evolving CMU’s AUIS• Version 6.3 to version 8• Five steps, approximately 800 refactorings, 14K lines of code

modified

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Contents: Detail

• Lessons Learned from experiments– Refactoring benefits– Refactoring limitations– Future research– Implication for Java

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Related Work

• Bergstein: Object-preserving class transformations• Lieberherr: Object-extending class transformations

– In the Demeter OO software environment

• Opdyke: Refactoring definition• Refactorings were inspired by

– Banerjee and Kim: Schema evolutions– Johnson and Foote: Design principles– UIUC Choices operating system

• L. Tokuda: Refactorings implementation for C++• D. Roberts: Refactorings implementation for Smalltalk and design criteria for transformation tools• Pree: Hot spot meta patterns

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Future Work

• Granularity of transformation– Larger grain refactorings?

• Program families– How to transform a file used by multiple programs

– How to cope with different pre-processed versions of a single C++ file

• Integration with other tools– e.g. RationalRose, IDE

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Contributions and Novelties

• Implemented a set of refactorings

• Experimental studies– Showed refactorings can scale and useful on large,

real-world applications

– Revealed the benefits, limitations and research problems

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What I like

• Refactoring– Manipulate code in a safe environment– Recreate s situation where evolution is possible– Help to understand existing code

• The paper– Clear and concise– Helpful diagrams– Two meaningful examples

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What I don’t like

• Refactoring– It’s hard to detect if a program needs to be refactored

– Refactorings depends on a specific language and compiler

– May slow down the execution

• The Paper– Lack of explanation of refactorings and their enabling

conditions

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Discuss

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Question 1

What is refactoring?

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Answer 1

Refactoring is the process of changing a software

system in such a way that it does not alter the external

behavior of the code yet improves its internal structure.

– Martin Fowler

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Question 2

How does refactorings preserve behavior?

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Answer 2

Identify and satisfy a list of enabling conditions

for each refactorings(i.e. pre-conditions).

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Question 3

Explain the benefits of refactoring.

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Answer 3

• Automating design change• Reduce testing• Simpler design• Validation assistance• Ease of exploration• Re-use existing software

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Question 4

Explain the problems that the current refactoring

technique is facing.

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Answer 4

• Refactoring is risky(source code changing may introduce subtle bugs)

• Refactorings are dependent on a specific language and compiler(preprocessor directives)

• Program families

• Source codes have to be accessible

• Conservative enabling conditions(if it is too conservative, the transformation might be useless)

• Automated checking of enabling conditions

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Question 5

What are the prerequisites for a programmer

to refactor a program properly?

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Answer 5

• The programmer has to know what the program does and how it is structureed

• Know what he wants to change and how it can be completed

• Know what a particular refactoring does and what are the enabling conditions

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Question 6

What problems do program families cause in

refactoring?

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Answer 6

When transforming a file used by more than one program, it

is desirable for the transformation system to check enabling

conditions for all programs in which use that file. Otherwise,

a file might be transformed safely for one program while

causing another program which uses the same file to break.

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Question 7

What features of Java make its refactorings have

easier implementations than C++?

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Answer 7

• NO preprocessor• Not use makefile• Code placement is simplified since methods are stores

in a file belongs to the class• No free-floating procedures

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Question 8

Discuss the possible practical improvement of

refactorings.

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Answer 8

• Specify refactorings in a language-independent manner

• Apply refactorings at higher levels of abstraction

• Integrate refactoring with other tools• Automatically determine where and what

refactorings should be applied• Solve program families problem

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Question 9

Discuss the connections between AOP and

Refactoring.

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Answer 9

• AOP is a tool for expressing code in a structured form

• Refactoring is a tool changing the structure of existing code, hopefully to improve it

• In some case may achieve a better refactoring using AOP

• AOP can be used on either existing or new code

• Refactoring only can be used on existing code

• AOP might reduce the chance of refactoring?

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Question 10

How can we determine where and why refactorings

should be applied?

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Answer 10

• Identify bad smells– Using Logic Meta Programming

– Other method?

• Future automatic tool