1 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

2 Paper Overview

3 Contents: Overview Roughly five parts: Introduction Overview of Refactorings Examples of Evolving Applications Lessons Learned from experiments Related work and Conclusion

4 Contents: Detail Introductio –Automate design level changes of source code –Preserve behavior

5 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

6 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

7 Contents: Detail Lessons Learned from experiments –Refactoring benefits –Refactoring limitations –Future research –Implication for Java

8 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

9 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

10 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

11 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

12 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

13 Discuss

14 Question 1 What is refactoring?

15 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

16 Question 2 How does refactorings preserve behavior?

17 Answer 2 Identify and satisfy a list of enabling conditions for each refactorings(i.e. pre-conditions).

18 Question 3 Explain the benefits of refactoring.

19 Answer 3 Automating design change Reduce testing Simpler design Validation assistance Ease of exploration Re-use existing software

20 Question 4 Explain the problems that the current refactoring technique is facing.

21 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

22 Question 5 What are the prerequisites for a programmer to refactor a program properly?

23 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

24 Question 6 What problems do program families cause in refactoring?

25 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.

26 Question 7 What features of Java make its refactorings have easier implementations than C++?

27 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

28 Question 8 Discuss the possible practical improvement of refactorings.

29 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

30 Question 9 Discuss the connections between AOP and Refactoring.

31 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?

32 Question 10 How can we determine where and why refactorings should be applied?

33 Answer 10 Identify bad smells –Using Logic Meta Programming –Other method? Future automatic tool