A Tool Support to Merge Similar Methods with a Cohesion Metric COB
37
A Tool Support to Merge Similar Methods with a Cohesion Metric COB ○ Masakazu Ioka 1 , Norihiro Yoshida 2 , Tomoo Masai 1 ,Yoshiki Higo 1 , Katsuro Inoue 1 1 Osaka University 2 Nara Institute of Science and Technology
description
A Tool Support to Merge Similar Methods with a Cohesion Metric COB. ○ Masakazu Ioka 1 , Norihiro Yoshida 2 , Tomoo Masai 1 ,Yoshiki Higo 1 , Katsuro Inoue 1 1 Osaka University 2 Nara Institute of Science and Technology. Refactoring with Eclipse. - PowerPoint PPT Presentation
Transcript of A Tool Support to Merge Similar Methods with a Cohesion Metric COB
A Tool Support to Merge Similar Methods with a Cohesion Metric COB
○ Masakazu Ioka1, Norihiro Yoshida2,Tomoo Masai1,Yoshiki Higo1, Katsuro Inoue1
1Osaka University2Nara Institute of Science and Technology
2
Refactoring with Eclipse
• It is easy to perform extract method refactoring by using Eclipse.
3
Refactoring for Similar Code Fragments
• Developers would like to merge similar code fragments for refactoring.– Developers need to modify only one code fragment
after merging
Modify
Merge
Modify
However, Eclipse doesn’t support this code modification.
4
An Example of Similar Code Fragments
float answer() { int a = getAve(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
float answer() { int a = getMax(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
5
Refactoring Candidate 1
float answer() { int a = getAve(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
float answer() { int a = getMax(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
6
Refactoring Candidate 2
float answer() { int a = getAve(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
float answer() { int a = getMax(); int b = getBase(); float ans;
if(a > b) { ans = a / b; print(ans); } else { ans = b / a; print(ans); } return ans;}
Extracted methods will be similar methods
7
Motivation
• It is difficult to decide which part is extracted.• If similar code fragments include multiple
differences, it is more difficult.
Which is better?
Cand.1 Cand.2 Cand.3
Show better candidates.
8
Form Template Method
• Refactoring pattern based on Template Method pattern [1].– Merge similar code fragments including differences.
[1] M. Fowler. Refactoring: Improving the Design of Existing Code. Addison Wesley, 1999.
Merge
9
Template Method
void select() ｛ input(); sort(); output();}
Override
Override// quick sortvoid sort();
Subclass B
Subclass A
// merge sortvoid sort();
// bubble sortvoid sort();
Subclass COverride
10
An Example of Form Template Method
…double base = _units*_rate*0.5;double tax = base*Site.TAX_RATE*0.2;return base + tax;
Site
ResidentialSite
getBillableAmount()
LifelineSite
getBillableAmount()
…double base = _units*_rate;double tax = base*Site.TAX_RATE;return base + tax;
11
An Example of Form Template MethodStep1: Detection of Primitive Processes
…double base = _units*_rate*0.5;double tax = base*Site.TAX_RATE*0.2;return base + tax;
Site
ResidentialSite
getBillableAmount()
LifelineSite
getBillableAmount()
…double base = _units*_rate;double tax = base*Site.TAX_RATE;return base + tax;
Detecting differences
Detecting primitive processes from differences
Primitive processes
12
An Example of Form Template MethodStep2: Extracting Primitive Processes
…double base = getBaseAmount();double tax = getTaxAmount();return base + tax;
Site
ResidentialSite
getBillableAmount()getBaseAmount()getTaxAmount()
LifelineSite
getBillableAmount()getBaseAmount()getTaxAmount()
…double base = getBaseAmount();double tax = getTaxAmount();return base + tax;
Extracting as methods
13
An Example of Form Template MethodStep3: Pulling-Up Similar Methods
Site
ResidentialSite
getBaseAmount()getTaxAmount()
LifelineSite
getBaseAmount()getTaxAmount()
getBillableAmount()getBaseAmount()getTaxAmount()
…double base = getBaseAmount();double tax = getTaxAmount();return base + tax;
Defining abstract methods at super class
Pulling-Up to super class
14
• It is difficult for developers to identify the common parts and the primitive processes from similar code fragments.– Developers need experience of Form Template Method
and knowledge of software.
A Problem of Form Template Method
Which is better?
Cand.1 Cand.2 Cand.3
• Showing candidates of Form Template Method in order of high cohesion.– When a method has high cohesion, the method may
have a single functionality.
Research Goal
15
[2] T. Miyake et al. “A software metric for identifying extract method candidates”, IEICE Trans. Inf.& Syst.(Japanese Edition) , 2009
Proposed Approach
Similar MethodsCOB = 0.9 COB = 0.2 COB = 0.75
1st 3rd 2ndCand.1 Cand.2 Cand.3
Cand.1 is better!!
Input: Similar methodsOutput: Ranked candidates of Form Template Method
Step1
Step2
Rank based on COB [2]
16
17
Step1: Detecting Differences between Similar Methods
Similar methods
b
C
e
B
a
C
d e
A
Compare Differenceson AST
Detect
Detect
Differences onsource code
a
C
d e
A
b
C
e
B
generate
generate
18
Step1: Generating Candidatesof Form Template Method
Verify extractableusing Eclipse JDT
Differences onsource code
Filter out wide range extraction candidates
Developers don’t know which candidate is better.
• It is necessary for Form Template Method to be exact match methods after extracting differences (Cond.1, 2).
• A method should have a single functionality (Cond.3).
Conditions of Appropriate Divisions
Cond.1: Each primitive process is extractable as method.Cond.2: A pair of similar code fragments is match after extraction.Cond.3: Extracted method has functionality for each developer.
Conditions of division on this research
19
20
An Example of Unsatisfying Any Conditions
void initTriangle(int x) { ．．． if(z > 0) { s = getArea(); t = s * getRate(); result = calc(s, t); print(result); } draw(); ．．．}
void initRectangle (int x) { ．．． if(z > 0) { s = getBase(); t = getRate(); result = calc(s, t); print(result); } draw(); ．．．}Unsatisfied division of
Cond.3
Different code fragment
Cond.3: Extracted method has functionality for each developers.
21
An Example of Satisfying All Conditions
void initTriangle(int x) { ．．． if(z > 0) { s = getArea(); t = s * getRate(); result = calc(s, t); print(result); } draw(); ．．．}
void initRectangle (int x) { ．．． if(z > 0) { s = getBase(); t = getRate(); result = calc(s, t); print(result); } draw(); ．．．}Satisfied division of
Cond.3
Different code fragment
Cond.3: Extracted method has functionality for each developers.
22
COB: Cohesion Of Blocks
• Evaluates cohesion between blocks– When a method has higher cohesion, the method
may have a single functionality.
b : the number of code blocks.v : the number of used variables in the method.: j-th variable used in the method.: the number of code blocks using variable .
23
void method() {int v1, v2, v3,
v4;BLOCK1 {
v1 = v1 + v2;
} BLOCK2 {
v2 = v1++;}
BLOCK3 {v3 = v3 *
v4;}
BLOCK4 {v4 = v3 +
1;}
}
An Example of Low COB
v １ v2 v3 v4
BLOCK1 ✓ ✓
BLOCK2 ✓ ✓
BLOCK3 ✓ ✓
BLOCK4 ✓ ✓
COB = 0.5
24
void method() {int v1, v2, v3;BLOCK1 {
v1 = v1 + v2;
} BLOCK2 {
v2 = v1++;}
BLOCK3 {v3 = v3 *
v1;}
BLOCK4 {v1 = v3 +
1;}
}
An Example of High COB
COB = 0.66
v １ v2 v3 v4
BLOCK1 ✓ ✓
BLOCK2 ✓ ✓
BLOCK3 ✓ ✓
BLOCK4 ✓ ✓
Replaced v4 with v1Replaced v4 with v1
25
Step2: Ranking Candidates of Form Template Method
COB = 0.4 COB = 0.2 COB = 0.8
Calculate COB
1st 3rd2nd
26
DemonstrationSelect menu
Input: Two methodsOutput: Ranked candidates of Form Template Method
26
Target methods
27
Demonstration - Select Target Class -
Select target class
27
28
Demonstration - Select Target Method -
Select target method
Select another method in the same way
28
29
Demonstration - First Candidate-
Corresponding extraction code
fragments
Extracting into children classes as same name method
Generating all candidates
30
Demonstration - All Candidates-
30
Caption of each tab means the order of rank based on metric COB.
31
Related Work (1/3)
• Juillerat et al. proposed an approach of automatic “Form Template Method” [3].
[3] N. Juillerat et al. Toward an Implementation of the “Form Template Method” Refactoring, 2007.
32
Related Work (2/3)
Similar methods
a
C
d e
A
b
C
e
B
Compare Differences onsource code
[○, □, a, A, □, ○, □, d, e, C, □, □]
[○, □, b, B, □, ○, □, e, C, □, □]
Our approach compares abstract syntax trees.
33
Related Work (3/3)
Differences onsource code
Only one candidate
Our approach shows many candidates in order of COB.
34
Conclusion and Future Work
• Conclusion– We proposed the tool that shows Good Candidates of
Form Template Method by cohesion metric COB.• Future Work
– How to decide a threshold for filtering.
35
Thank You for Listening
36
37
