The relevance of code refactoring and our journey to develop a tool for automatic Java refactoring, jSparrow.

1. A journey to automatic Java refactoring
Software Quality Days 2019
Martin Huter & Ardit Ymeri
A journey to automatic Java
refactoring (and jSparrow)

2. A journey to automatic Java refactoring
Who are we?
Slide 2

3. A journey to automatic Java refactoring
Agenda
▪ Refactoring
▪ Software aiding the refactoring process
▪ Creating an automatic refactoring tool
Slide 3

4. A journey to automatic Java refactoring
Management: Do we really need that?
Refactoring
Slide 4

5. A journey to automatic Java refactoring
What is Refactoring
Slide 5
▪ Changing the code and keeping functionality
▪ Reasons include
▪ Improve readability
▪ Reduce complexity
▪ Improve maintainability
▪ Improve internal architecture
▪ Improve performance
▪ Improve security
▪ Parallelization

6. A journey to automatic Java refactoring
Typical Problems
▪ Design and code structure
▪ Lack of Cohesion
▪ Tight Coupling
▪ Repeated Code
▪ Spaghetti Code
▪ Lack of Performance
▪ Lack of Tests
▪ Security Issues
Slide 6

7. A journey to automatic Java refactoring
Human Approach
▪ Define a goal
▪ Understand the code base
▪ Set up a safety net - Tests!
▪ Refactor
▪ Go with baby steps
▪ Test
▪ Does everything still work?
▪ Repeat
Slide 7
Refactor
Test

8. A journey to automatic Java refactoring
Preserving Functionality
▪ Testing helps - but never guarantees.
▪ Program Equivalence
▪ Do programs P and Q terminate on the same state when starting on the same
one?
▪ Reducible to the Halting Problem.
▪ Undecidable!!!
▪ All nontrivial semantic properties are undecidable 👉 Rice’s Theorem
▪ The good news: Undecidable only in general!
▪ Show correctness for specific cases
▪ Trivial properties are decidable.
Slide 8

9. A journey to automatic Java refactoring
Using Functional Interfaces
Slide 9
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
passwordField.requestFocusInWindow();
passwordField.requestFocus();
}
});
SwingUtilities.invokeLater(() -> {
passwordField.requestFocusInWindow();
passwordField.requestFocus();
});

10. A journey to automatic Java refactoring
Using Standard Outputs
Slide 10
System.err.println(e.getMessage());
logger.error(e.getMessage());
e.printStackTrace();
logger.error(e.getMessage(), e);

11. A journey to automatic Java refactoring
Cognitive Complexity
Slide 11
public void remapIds() {
Attribute idAttribute = getAttributes();
if (idAttribute != null) {
// very long code
…
}
}
public void remapIds() {
Attribute idAttribute = getAttributes();
if (idAttribute == null) {
return;
}
// very long code
…
}

12. A journey to automatic Java refactoring
Other Code Smells
Slide 12
▪ Methods should not be empty
▪ Deprecated code should be removed
▪ Sections of code should not be commented out
@Deprecated
public static void doSomething(Object changeMe) {
// throw new UnsupportedOperationException();
}

13. A journey to automatic Java refactoring
There is Software that might help
Help me?
Slide 13

14. A journey to automatic Java refactoring
Assessing Technical Debt
Slide 14
▪ Existing Solutions
▪ Integration in development process
▪ Reporting technical debt
▪ Evaluating efforts

15. A journey to automatic Java refactoring
Addressing Technical Debt
Common scenarios for 100k lines
▪ 10s Thousands issues
▪ Hundreds working days
Addressing by:
▪ Avoid creating more debt
▪ Continuously removing debt
▪ Automatically resolving issues
Slide 15

16. A journey to automatic Java refactoring
Resolving Automatically
▪ Spotting issues
▪ Generating refactored code
▪ Avoiding Conflicts
▪ Preserving Functionality
▪ Test automation
▪ Preserving Comments
Slide 16

17. A journey to automatic Java refactoring
From Spotting to fixing
Can I automate that?
Slide 17

18. A journey to automatic Java refactoring
Change source with AST
Slide 18
1
Parsing
source
to
AST
Firstyou
need
a
toolthatw
illparse
your
source
code
like
a
com
piler
2
M
anipulating
AST
Use
the
resulting
AST
to
adoptthe
code
and
apply
fixes
3
Assure
syntax
stillvalid
Verify
changes
resultin
a
valid
source
code
4
W
riting
Changes
Apply
the
changes
to
the
source
file
and
replace
it

19. A journey to automatic Java refactoring
What framework to use?
Slide 19
Java Grammar Java Compiler Advantages of the Framework
● Open source
● Integrated within Eclipse IDE
1 Eclipse JDT
● Open source
● Integrated within Intellij IDE
2 Javaparser.org
● Mostly independent
● Building a lot from scratch
3 Antlr 4

20. A journey to automatic Java refactoring
jSparrow
Slide 20
Eclipse JDT
Eclipse Plugin
GitHub App
Maven Plugin

21. A journey to automatic Java refactoring
Automatic Refactoring
● Pros
+ Save time
+ Reduce debt
+ Set standards
+ Integration in development process
+ Improve coding habits
● Cons
- Technical restrictions
Slide 21

22. A journey to automatic Java refactoring
jSparrow Features
▪ 53 Rules and growing
▪ Custom rule profiles
▪ Portable between platforms
▪ Built-in review functionality
Slide 22

23. A journey to automatic Java refactoring
The end
▪ Thanks for your time, we now got some time left to discuss
questions.
▪ You can also visit us at our booth at number 13
Slide 23