Commonality and Variability Analysis: Avoiding Duplicate Code

The First 100 Hours:
Commonality and
Variability Analysis

Jason Cheong-Kee-You
@jpcky www.mightyjupiter.com

Alistair McKinnell
@amckinnell www.valuablecode.com

Commonality and

Commonality and

Avoiding Duplicate Code

Exercise
1. Did you write any code last year?
If so, how many lines of code?
2. How many lines of code in your
code base?
3. Percentage of duplicate code?


DRY: Don’t Repeat Yourself


DRY: Don’t Repeat Yourself
Every piece of knowledge must have
a single, unambiguous, authoritative
representation within a system.


Once and Only Once


Once and Only Once
Data, structure, or logic should exist
in only one place in the system.


Test-Driven Development


1. Write new code only if an
automated test has failed.


1. Write new code only if an
automated test has failed.
2. Eliminate duplication.


Single Choice Principle


Whenever a software system must
support a set of alternatives, one
and only one module in the system
should know their exhaustive list.


Duplication may be the
root of all evil in software.

Exercise

What are the consequences of
duplicate code?

Exercise

What are the consequences of
duplicate code?

Consider both good and evil.

Exercise

How does duplicate code
come about?

Exercise

How does duplicate code
come about?

Make a Top 3 list.

Commonality and Variability Analysis: Avoiding Duplicate Code

Alistair’s Contention
Copy and Paste leads to the
creation of duplicate code.

Alistair’s Contention
Copy and Paste leads to the
creation of duplicate code.
Developers lack the thinking tools
and the development skills to avoid
the duplication.

Duplicate Code:
Select Options

Select Options
public static List<SelectOption> createEndMonthList(Date expiryDate) {
List<SelectOption> monthList = new ArrayList<SelectOption>();
int month = getDateMonth(expiryDate);
for (int intLooper = 1; intLooper <= 12; intLooper++) {
SelectOption option = new SelectOption();
if (month == intLooper) {
option.setLabel(String.valueOf(intLooper));
option.setValue(String.valueOf(intLooper));
option.setSelected(true);
} else {
option.setValue(String.valueOf(intLooper));
option.setSelected(false);
}
monthList.add(option);
}
return monthList;
}

Select Options
SelectOptions SelectOptionsSource

create() getFirst()
getLast()
isSelected()

Commonality Variability Resolution

Data Structure Value of State Simple Java Type

Select Options

create() getFirst()
getLast()
isSelected()

Parameter
Object

Select Options

create() getFirst()
getLast()
isSelected()

Encapsulate
Behaviour Collaborator
Collection

Select Options

create() getFirst()
getLast()
isSelected()

Encapsulate
Collection

Duplicate Code:
Select Options Extra

public static List<SelectOption> createProvinceList(String selectedProvince)
{
List<SelectOption> provinceList = new ArrayList<SelectOption>();

List<String> provinces = asList("AB", "BC", "MB", "NB", "NL",
"NT", "NS", "NU", "ON", "PE", "QC", "SK", "YT");

for (int intLooper = 0; intLooper < provinces.size(); intLooper++) {
if (selectedProvince.equals(provinces.get(intLooper))) {
option.setLabel(provinces.get(intLooper));
option.setValue(provinces.get(intLooper));
option.setSelected(true);
} else {
option.setValue(provinces.get(intLooper));
option.setSelected(false);
}
provinceList.add(option);
}
return provinceList;
}


public enum Province {
AB, BC, MB, NB, NL, NT, NS, NU, ON, PE, QC, SK, YT;
}

A small set of
Data Structure enum
values

public enum Province {
AB, BC, MB, NB, NL, NT, NS, NU, ON, PE, QC, SK, YT;
}

Whenever a software system must
support a set of alternatives, one
and only one module in the system
should know their exhaustive list.

public static List<SelectOption> createEndMonthList(Date expiryDate) {

for (int intLooper = 1; intLooper <= 12; intLooper++) {
if (month == intLooper) {

}

public static List<SelectOption> createProvinceList(String selectedProvince)
{

for (int intLooper = 0; intLooper < provinces.size(); intLooper++) {
if (selectedProvince.equals(provinces.get(intLooper))) {

}

String
Iterable

iterator()


create() isSelected()

IntegerRangeSource ProvinceSource

iterator() iterator()
isSelected() isSelected()

String
Iterable

iterator()






Collection Values Iterator

String
Iterable

iterator()






Collection Type Generics

String
Iterable

iterator()





Inheritance
Behaviour Implementation
(Object-Oriented)

Duplicate Code:
Compound Result Handler

public Collection<IRegCommand> processCompondResults(Patient sourcePatient, Collection<Result> results) {
Collection<IRegCommand> retVal = new ArrayList<IRegCommand>();
Set<Result> resultsMarkedForRemoval = new HashSet<Result>();
Set<Result> resultsProcessed = new HashSet<Result>();

for (Result primaryResult : results) {
if (isResultProcessed(resultsProcessed, primaryResult)) {
continue;
}

resultsProcessed.add(primaryResult);
Result correspondingResult = getCorrespondingResult(primaryResult, results);

if (correspondingResult != null) {
resultsProcessed.add(correspondingResult);
resultsMarkedForRemoval.add(correspondingResult);
}

if (!sourcePatient.getDataWarehouse().equals(DataWarehouseTag.QHN)) {
// If the response to either question is yes then display positive as the measure value.
if (primaryResult.getDwValue().equalsIgnoreCase("1")) {
primaryResult.setDwValue("POSITIVE");
} else {
// If the response to both questions is no then display negative as the measure value.
if (correspondingResult.getDwValue().equalsIgnoreCase("2")) {
primaryResult.setDwValue("NEGATIVE");
} else if (correspondingResult.getDwValue().equalsIgnoreCase("1")) {
// It must be yes - thus value is POSITIVE
} else {
badDataLogger.logBadData(sourcePatient.getExternalId(), Measure.NAME_2ITEMSCREENER,
primaryResult.getDwValue() + " (" + primaryResult.getEventDateTime() + ") ",
"Issue with multiple PHQ results");
continue;
}
} else {
// No corresponding result - where is the 2nd result? -
"No corresponding value found for a 2 item screener with value of 'no'");
continue;
}
}
} else {
if (primaryResult.getDwValue().equalsIgnoreCase("3") ||
primaryResult.getDwValue().equalsIgnoreCase("4")) {
} else {
primaryResult.getDwValue().equalsIgnoreCase("1") ||
} else if (primaryResult.getDwValue().equalsIgnoreCase("3") ||
} else {
continue;
}
} else {
continue;
}
}
}

Map<String, Object> transformedResult = resultTransformer.transformResult(sourcePatient, primaryResult);

if (null != transformedResult) {
retVal.add(new PatientDataUpdateCommand(CommandType.RESULT, sourcePatient, transformedResult));
}
}

return retVal;
}


continue;
}



}
if (!sourcePatient.getDataWarehouse()
.equals(DataWarehouseTag.QHN)) {
} else {
} else {
continue;
}
} else {
continue;
}
}
} else {
} else {
} else {
continue;
}
} else {
continue;
}
}
}


}
}

return retVal;
}


continue;
}



}

if (primaryResult.getDwValue().equalsIgnoreCase("1"))
} else {
} else {
continue;
}
} else {
continue;

}
} else {
}
primaryResult.getDwValue().equalsIgnoreCase("4"))
} else {
} else {
continue;
}
} else {
continue;
}
}
}


}
}

return retVal;
}

CompoundResultHandler CompoundResultClassifier

isNegative()
isPositive()

AbstractCompoundResultClassifier

toNumber()

QueensCompoundResultClassifier StandardCompoundResultClassifier

isNegative() isNegative()
isPositive() isPositive()


isNegative()
isPositive()


toNumber()



Inheritance
Behaviour Implementation
(Object-Oriented)


isNegative()
isPositive()


toNumber()




Implementation None Base Class

Reading
The Pragmatic Programmer: From Journeyman to Master
Andrew Hunt and Dave Thomas

Extreme Programming Explained: Embrace Change
Kent Beck and Cynthia Andres

Test Driven Development: By Example
Kent Beck

Object-Oriented Software Construction
Bertrand Meyer

Reading
Clean Code: A Handbook of Agile Software
Craftsmanship Robert C. Martin

Design Patterns: Elements of Reusable Object-Oriented
Software Erich Gamma, Richard Helm, Ralph Johnson,
and John Vlissides

Multi-Paradigm Design for C++
James O. Coplien

Lean Architecture: for Agile Software Development
James O. Coplien and Gertrud Bjørnvig

Photo Credits
http://www.flickr.com/photos/27558040@N00/4151899795/

http://www.flickr.com/photos/popilop/331357312/

http://www.flickr.com/photos/arlette/3260468/

http://www.flickr.com/photos/36829973@N04/3546657245/

Commonality and Variability Analysis: Avoiding Duplicate Code

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Editor's Notes