Investigation of Coding Patterns over Version History

Software Engineering Laboratory, Department of Computer Science, Graduate School of Information Science and Technology, Osaka University

Investigation of Coding Patterns over Version History

Hironori Date, Takashi Ishio, Katsuro Inoue

Osaka University, Japan

Department of Computer Science, Graduate School of Information Science and Technology, Osaka University

Coding Patterns

• Frequent sequence of call elements and control elements– Call element

• Method call element• Constructor call element

– Control element• IF, END-IF• LOOP, END-LOOP

etc…• Implement a particular kind of

concerns– spread around source code

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JHotDraw Ver. 5.4b1


Previous Research [1]

• Extracted coding patterns from 5 applications• Coding pattern type

– API usage patterns– Application-specific Patterns

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[1] T. Ishio, H. Date, T. Miyake, and K. Inoue, “Mining coding patterns to detect crosscutting concerns in java programs,” in Proceedings of the 15th Working Conference on Reverse Engineering, 2008, pp. 123–132.

Coding patterns are candidates of reusable code


Previous Research [1]

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?? ??

Similar Patterns

<a(), b()> <a(), b(), c()>

<a(), c(), b()>

<IF, a(), b(), END-IF>

Which patterns are easier to reuse?

Assumption: Stable patterns are reusable


Research Question

To answer this question …1. Extract coding patterns from multiple

versions of applications2. Investigate the life-span of coding patterns

Life-span: the number of versions where we find the identical pattern

Are the coding patterns generally stable

over the version history?

RQ

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Outline of Experiment

• Mining coding patterns 1. Normalization of source

code2. Sequential pattern

mining for each version• Tracking coding patterns

– Compute life-span of each pattern

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.java.java.java .jav

a.java.java.jav

a.java.java

.xml .xml .xml…

…

Ver. 1 Ver. 2 Ver. N

Source Code

Coding Patterns

Ver. 1 Ver. 2 … Ver. N Life-span

Pat. 1 3 4 … 3 6

Pat. 2 0 0 … 2 4

… … … … … …

Pat. M 3 0 … 2 3

Life-span

Mining Coding Patterns(using Fung)

Tracking Coding Patterns







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a.java.java.jav

a.java.java

.xml .xml .xml…

…


Source Code

Coding Patterns


Pat. 1 3 4 … 3 6

Pat. 2 0 0 … 2 4

… … … … … …

Pat. M 3 0 … 2 3

Life-span









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a.java.java.jav

a.java.java

.xml .xml .xml…

…


Source Code

Coding Patterns


Pat. 1 3 4 … 3 6

Pat. 2 0 0 … 2 4

… … … … … …

Pat. M 3 0 … 2 3

Life-span




Normalization in Pattern Mining

• Translate each method into a sequence– Call elements– Control elements

• Normalize control elements (Table I)

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public class A { void a() { int i = x + y; callA(); callB(); callB(); }

void b() { if (cond()) { callA(); callB(); } }}

Source File Sequence Database

<callA(), callB(), callB()>

<cond(), IF, callA(), callB(), END-IF>

A.a()

A.b()

Norm

alization


public class A { void a() { int i = x + y; callA(); callB(); callB(); }

void b() { if (cond()) { callA(); callB(); } }}

Source File

Norm

alization

Coding Pattern

Sequential Pattern Mining

Sequence Database

<callA(), callB(), callB()>

<cond(), IF, callA(), callB(), END-IF>

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A.a()

A.b()

Sequential Pattern Mining

• Minimum Length: 2 threshold of #pattern element • Minimum Support: 2 threshold of #pattern instance

class A { void a() { … }}

class A { void b() { … }}

<callA(), callB()>

Parameters

Department of Computer Science, Graduate School of Information Science and Technology, Osaka University11

Identical Patterns Between Versions

• Exact match of pattern sequence

• Not care #instance

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<a(), b(), c()>

Ver. X Ver. Y

<a(), b(), c(), d()>

<a(), b(), c()>

… …


class B { void b() { … }}





class C { void c() { … }}





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<a(), b(), c()>

Ver. X Ver. Y

<a(), b(), c(), d()>

<a(), b(), c()>

… …








NOT Identical





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<a(), b(), c()>

Ver. X Ver. Y

<a(), b(), c(), d()>

<a(), b(), c()>

… …








Identical



1. List all of coding patterns from all versions2. Look up #pattern instance in each version3. Compute life-span

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Ver. 1 Ver. 2 Ver. 3 Life-span<a(), b()> 2 3 3 3

<IF, b(), c(), END-IF> 0 0 2 1<a(), IF, d(), ELSE, c(), END-IF> 4 2 3 3

<d(), e(), f()> 2 0 2 2

Ver. 1 Ver. 2 Ver. 3

.xml .xml.xml

Pattern Version

Coding Patterns




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Ver. 1 Ver. 2 Ver. 3 Life-span<a(), b()>

<IF, b(), c(), END-IF>

<a(), IF, d(), ELSE, c(), END-IF>

<d(), e(), f()>


.xml .xml.xml

Pattern Version

Coding Patterns




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Ver. 1 Ver. 2 Ver. 3 Life-span<a(), b()>



<d(), e(), f()>


.xml .xml.xml

Pattern Version

Coding Patterns





<d(), e(), f()>

Pattern Version


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Coding Patterns


.xml .xml.xml

V

<a(), b()>





class B{ void b() { … }}




class B{ void b() { … }}2 instances

3 instances

3 instances

Coding Patterns



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Coding Patterns


.xml .xml.xml

V



class B{ void b() { … }}Not Found

Not Found

2 instances


<IF, b(), c(), END-IF> 0 0 2 1<a(), IF, d(), ELSE, c(), END-IF>

<d(), e(), f()>

Pattern Version


Coding Patterns



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Coding Patterns


.xml .xml.xml

V










class D { void d() { … }}4 instances

2 instances

3 instances



<d(), e(), f()>

Pattern Version


Coding Patterns



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Coding Patterns


.xml .xml.xml

V



class B{ void b() { … }}Not Foundclass A {

void a() { … }}

class B{ void b() { … }}2 instances

2 instances



<d(), e(), f()> 2 0 2 2

Pattern Version

<d(), e(), f()>

Coding Patterns


Experiments• Target applications

download source archive of release versions from project web sites– dnsjava

Version: 0.1 to 2.0.1 (51 versions)– JmDNS

Version: 0.2 to 3.4.1 (20 versions)

• Pattern mining parameters– Minimum length: 2

• Threshold of the number of elements of a pattern sequence– Minimum support: 2

• Threshold of the number of pattern instances

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Result of Experiment

• LOC and the number of patterns– Figure 2 and Figure 3

• Distribution of life-span– Figure 4 and Figure 5

• Distribution of life-span and pattern length– Figure 6 and Figure 7

• Show sample code of patterns with longest life-span– Picked up from Table III and Table IV

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LOC and the Number of Patternsin dnsjava (Figure 2)

• 51 versions• 5,084 LOC to 33,330 LOC• 512 to 4,405 patterns (in single version)• 17,284 patterns in total (no duplication)• The correlation coefficients (LOC & #Pattern): 0.912

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0

1000

2000

3000

4000

5000

0

5000

10000

15000

20000

25000

30000

35000

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.8.1

0.8.2

0.8.3

0.9

0.9.1

0.9.2

0.9.3

0.9.4

0.9.5

1.0

1.0.1

1.0.2

1.1

1.1.1

1.1.2

1.1.3

1.1.4

1.1.5

1.1.6

1.2.0

1.2.1

1.2.2

1.2.3

1.2.4

1.3.0

1.3.1

1.3.2

1.3.3

1.4.0

1.4.1

1.4.2

1.4.3

1.5.0

1.5.1

1.5.2

1.6.1

1.6.2

1.6.3

1.6.4

1.6.5

1.6.6

2.0.0

2.0.1

LOC

#Pattern

LOC #Pattern

Version


LOC and the Number of Patternsin JmDNS (Figure 3)

• 20 versions• 3,408 LOC to 17,252 LOC• 237 to 2,419 patterns (in single version)• 8,625 patterns in total (no duplication)• The correlation coefficients (LOC & #Pattern): 0.721

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0

500

1000

1500

2000

2500

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0.2

1.0.RC

11.0.RC

21.0-Final

2.0

2.1

3.0

3.1

3.1.2

3.1.3

3.1.4

3.1.5

3.1.6

3.1.7

3.1.8

3.2.0

3.2.1

3.2.2

3.4.0

3.4.1

LOC

#Pattern

LOC

#Pattern

Version


Life-span of Patterns in dnsjava (Figure 4)

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4929

3422

1591

1167

782

467

794647

377454320313273136

403

149134121228

48 43 51 29 44 26 25 30 39 25 19 24 20 13 16 14 13 5 6 5 8 3 10 7 21 8 1 1 4 5 0 140

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51

Median: 3

14 patterns appear in all versions(Table III)

Life-span

Frequency

Stable PatternUnstable Pattern

Total 17,284 patternsin 51 versions


Life-span of Patternsin JmDNS (Figure 5)

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21532244

1531

870

415 426357

50188

65 46 41 84 22 16 43 9 2 42 210

500

1000

1500

2000

2500

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Median: 2

21 patterns appear in all versions(Table IV)

Life-span

Frequency

Stable PatternUnstable Pattern

Total 8,625 patternsin 20 versions


Life-span of Patterns• dnsjava (51 versions)

– A half of coding pattern disappeared within 3 versions (median is 3)

• JmDNS (20 versions)– A half of coding pattern disappeared within 2 versions

(median is 2)

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Life-span of coding pattern tends to be short


Life-span and Pattern Length dnsjava (Figure 6)

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No Patterns

Coding patterns with short life-span include a small number of elements

Coding patterns with long life-span have short pattern length

Coding patterns

includes a large number of elements

survive only a short period


Life-span and Pattern LengthJmDNS (Figure 7)

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No Patterns

Coding patterns with long life-span have short pattern length

A lot of patterns with short life-span include a small number of elements

Coding patterns includes a large number of elementssurvive only a short period


Stable Patterns in dnsjava

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Stable Pattern in dnsjavaApplication-specific pattern

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public SetResponseaddMessage(Message in) {

boolean isAuth = in.getHeader().getFlag(Flags.AA);Record question = in.getQuestion();Name qname;Name curname;int qtype;int qclass;int cred;int rcode = in.getHeader().getRcode();boolean haveAnswer = false;

...}

org.xbill.DNS.Cache (ver. 2.0.1)

<getHeader(), getRcode()> 5 instances in ver. 2.0.1


Stable Pattern in dnsjavaObject generation pattern

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private voidfindResolvConf(String file) {

InputStream in = null;try {

in = new FileInputStream(file);}catch (FileNotFoundException e) {

return;}InputStreamReader isr = new InputStreamReader(in);BufferedReader br = new BufferedReader(isr);

...}

org.xbill.DNS.spi.ResolverConfig (ver. 2.0.1)

<java.io.InputStreamReader.<init>(java.io.InputStream), java.io.BufferedReader.<init>(java.io.Reader)> 5 instances in ver. 2.0.1


Stable Pattern in dnsjavaIteration related idiom

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protected DNSJavaNameService() { ...

if (nameServers != null) {StringTokenizer st = new StringTokenizer(nameServers, ",");String [] servers = new String[st.countTokens()];int n = 0;while (st.hasMoreTokens())

servers[n++] = st.nextToken();try {

Resolver res = new ExtendedResolver(servers);Lookup.setDefaultResolver(res);

}catch (UnknownHostException e) {

...}

} ...} org.xbill.DNS.spi.DNSJavaNameService (ver. 2.0.1)

<hasMoreTokens(), LOOP, nextToken(), hasMoreTokens(), END-LOOP>6 instances in ver. 2.0.1


Stable Patterns in JmDNS

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Stable Pattern in JmDNSMulti-thread idiom with synchronized keyword

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public synchronized String getPropertyString(String name) { byte data[] = this.getProperties().get(name); if (data == null) { return null; } if (data == NO_VALUE) { return "true"; } return readUTF(data, 0, data.length);}

javax.jmdns.impl.ServiceInfoImpl (ver. 3.4.1)

<SYNCHRONIZED, getProperties(), get(java.lang.Object), END-SYNCHRONIZED>2 instances in ver.3.4.1


Answer the Research Question

• Coding patterns with short life-span account for a large part

• Few coding patterns with long life-span

Are the coding patterns generally stable

over the version history?

RQ

No, The coding patterns are NOT generally

stable.

Answer

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Conclusion• Investigation of the stability of coding patterns across

versions– Method

• Extract coding patterns from versions of code• Compute life-span

– Target• dnsjava (51 versions)• JmDNS (20 versions)

• Result– Coding patterns are not generally stable

• Coding patterns may not be suitable for reuse• Future work

– Further investigation with more applications

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Investigation of Coding Patterns over Version History

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