Metrics ekon 14_2_kleiner

Top Ten Metrics
10 print “hello EKON”;
20 Goto 10;

“Metrics measure the design of code after it
has been written”

1

Agenda EKON
• What are Metrics ?
• How to recognize Bad Code ?
• Top Ten (The Law of Demeter)
• Improve your Code (Metric Based Refactoring)
• Optimisation and other Tools

2

What are Metrics?
Metrics are for
• Evaluate Object Complexity
• Quantify your code
• Highlight Redesign Needs
• Change Impact Analysis

UEB: 15_pas_designbycontract.txt

3

Metrics deal with
Bad Structure
• General Code Size (in module)
• Cohesion (in classes and inheritance)
• Complexity
• Coupling (between classes or units)
• Cyclic Dependency, Declare+Definition, ACD-Metric
• Interfaces or Packages (design & runtime)
• Static, Public, Private (inheritance or delegate)

UEB: 10_pas_oodesign_solution.txt

4

Metric Context
Refactoring
DUnit

change
st
te

improve
Source Units
ie w
R ev
its
A ud
Metrics

5

Some Kind of wonderful ?
• statusbar1.simpletext
• simplepanel:= true!
• TLinarBitmap = TLinearBitmap; //Spelling bug
• aus Win32.VCL.Dialogs.pas
• WndProcPtrAtom: TAtom = 0;
• aus indy: self.sender!
• procedure TIdMessageSender_W(Self: TIdMessage;
const T: TIdEmailAddressItem);
• begin Self.Sender := T; end;

UEB: 8_pas_verwechselt.txt

6

When and why Metrics ?
After a Code Review
By changes of a release
Redesign with UML (Patterns or Profiles)
Law of Demeter not passed
Bad Testability (FAT or SAT)
• Work on little steps at a time
• Modify not only structure but also code format

7

What‘s Bad Code
Bad Coordination
• Inconsistence with Threads
• Access on objects with Null Pointer
• Bad Open/Close of Input/Output Streams or
I/O Connections
• Check return values or idempotence
• Check break /exit in loops
• Modification of static or const code
• Access of constructor on non initialized vars

8

Metric/Review Checklist
1. Standards - are the Pascal software standards for
name conventions being followed?
2. Are all program headers completed?
3. Are changes commented appropriately?
4. Are release notes Clear? Complete?
5. Installation Issues, Licenses, Certs. Are there any?
6. Version Control, Are output products clear?
7. Test Instructions - Are they any? Complete?
8. "Die andere Seite, sehr dunkel sie ist" - "Yoda, halt's Maul und iß
Deinen Toast!"

9

Top Ten Metrics
1. VOD Violation of Law of Demeter
2. Halstead NOpmd (Operands/Operators)
3. DAC (Data Abstraction Coupling)(Too many
responsibilities or references in the field)
4. CC (Complexity Report), McCabe cyclomatic
complexity, Decision Points)
5. CBO (Coupling between Objects) Modularity

10

Top Ten II
6. PUR (Package Usage Ratio) access information
in a package from outside
7. DD Dependency Dispersion (SS, Shotgun Surgery
(Little changes distributed over too many
objects or procedures patterns missed))
8. CR Comment Relation
9. MDC (Module Design Complexity (Class with too
many delegating methods)
10. NORM (remote methods called (Missing
polymorphism))

11

Law of Demeter
You should avoid:
• Large classes with strange members
•Das Gesetz von Demeter (don‘t talk to
strangers) besagt, dass ein Objekt O als
Reaktion auf eine Nachricht m, weitere
Nachrichten nur an die folgenden Objekte
senden sollte: (all objects to which m sends a
message must be instances of classes)

12

Demeter konkret
1. [M1] an Objekt O selbst
Bsp.: self.initChart(vdata);
2. [M2] an Objekte, die als Parameter in der Nachricht
m vorkommen
Bsp.: O.acceptmemberVisitor(visitor)
visitor.visitElementChartData;
3. [M3] an Objekte, die O als Reaktion auf m erstellt
Bsp.: visitor:= TChartVisitor.create(cData, madata);
4. [M4] an Objekte, auf die O direkt mit einem Member
zugreifen kann
Bsp.: O.Ctnr:= visitor.TotalStatistic

13

Demeter Test as SEQ

UEB: 56_pas_demeter.txt

14

DAC or Modules of Classes
Large classes with to many references
• More than seven or eight variables
• More than fifty methods
• You probably need to break up the class in
Components (Strategy, Composite, Decorator)
TWebModule1 = class(TWebModule)
HTTPSoapDispatcher1: THTTPSoapDispatcher;
HTTPSoapPascalInvoker1: THTTPSoapPascalInvoker;
WSDLHTMLPublish1: TWSDLHTMLPublish;
DataSetTableProducer1: TDataSetTableProducer;

15

CC
• Check Complexity
function IsInteger(TestThis: String): Boolean;
begin
try
StrToInt(TestThis);
except
on EConvertError do
result:= False;
else
result:= True;
end;
end;

16

CBO I
CBO measures the number of classes to which a class is
coupled. According to remarks and comments on CBO and
coupling, we include coupling through inheritance.

Two classes are considered coupled, if methods declared in
one class call methods or access attributes defined in the
other class.

17

CBO II
Are Business Objects available for good CBO (Extensions)?
In a simple business object (without fields in the class),
you do have at least 4 tasks to fulfil:

1. The Business-Class inherits from a Data-Provider
2. The query is part of the class
3. A calculation or business-rule has to be done
4. The object is independent from the GUI, GUI calls the
object “Business objects are sometimes referred to as conceptual objects,
because they provide services which meet business requirements,
regardless of technology”.

18

PUR Package Usage Ratio

19

Welche Metric? DD
• Dependency Dispersion (Code too much Distributed):
…..
for i:= 0 to SourceTable.FieldCount - 1 do
DestTable.Fields[i].Assign(SourceTable.Fields[i]);
DestTable.Post;
…..

20

DD – use small procedures
Procedure CopyRecord(const SourceTable, DestTable:
TTable);
var i: Word;
begin
DestTable.Append;
For i:= 0 to SourceTable.FieldCount - 1 do
DestTable.Fields[i].Assign(SourceTable.Fields[i]);
DestTable.Post;
end;

21

Finally you can measure:
Bad Naming (no naming convention)
Duplicated Code (side effects)
Long Methods (to much code)
Temporary Fields (confusion)
Long Parameter List (Object is missing)
Data Classes (no methods)
• Large Class with too many delegating methods
In a Kiviat Chart you get a Best Practices Circle!

UEB: 33_pas_cipher_file_1.txt

22

Why is Refactoring important?
• Only defense against software decay.
• Often needed to fix reusability bugs.
• Lets you add patterns or templates after you
have written a program;
• Lets you transform program into framework.
• Estimation of the value (capital) of code!
• Necessary for beautiful software.

23

Refactoring Process
The act of serialize the process:
Build unit test
Refactor and test the code (iterative!)
Check with Pascal Analyzer or another tool
Building the code
Running all unit tests
Generating the documentation
Deploying to a target machine
Performing a “smoke test” (just compile)

24

Let‘s practice
• 1
• 11
• 21
• 1211
• 111221
• 312211
• ??? Try to find the next pattern, look for
a rule or logic behind !

25

function runString(Vshow: string): string;
var i: byte;
Rword, tmpStr: string;
cntr, nCount: integer;
begin
cntr:=1; nCount:=0;
Before R.
Rword:=''; //initialize
tmpStr:=Vshow; // input last result
for i:= 1 to length(tmpStr) do begin
if i= length(tmpstr) then begin
if (tmpStr[i-1]=tmpStr[i]) then cntr:= cntr +1;
if cntr = 1 then nCount:= cntr
Rword:= Rword + intToStr(ncount) + tmpStr[i]
end else
if (tmpStr[i]=tmpStr[i+1]) then begin
cntr:= cntr +1;
nCount:= cntr;
end else begin
if cntr = 1 then cntr:=1 else cntr:=1; //reinit counter!
Rword:= Rword + intToStr(ncount) + tmpStr[i] //+ last char(tmpStr)
end;
end; // end for loop
result:=Rword;
end; UEB: 9_pas_umlrunner.txt

26

After R.
function charCounter(instr: string): string;
var i, cntr: integer; Rword: string;
begin
cntr:= 1;
Rword:=' ';
for i:= 1 to length(instr) do begin
//last number in line
if i= length(instr) then
concatChars()
else
if (instr[i]=instr[i+1]) then cntr:= cntr +1
else begin
concatChars()
//reinit counter!
cntr:= 1;
end;
end; //for
result:= Rword;
end;

UEB: 12_pas_umlrunner_solution.txt

27

Refactoring Techniken
Einheit Refactoring Funktion Beschreibung
Package Rename Package Umbenennen eines Packages
Class Move Method Verschieben einer Methode
Class Extract Superclass Aus Methoden, Eigenschaften eine
Oberklasse erzeugen und verwenden
Class Introduce Parameter Ersetzen eines Ausdrucks durch einen
Methodenparameter
Class Extract Method Heraustrennen einer Codepassage
Interface Extract Interface Aus Methoden ein Interface erzeugen
Interface Use Interface Erzeuge Referenzen auf Klasse

Component Replace Inheritance Ersetze vererbte Methoden durch
with Delegation Delegation in innere Klasse
Class Encapsulate Fields Getter- und Setter einbauen
Modell Safe Delete Löschen einer Klasse mit Referenzen

28

Metric based Refactoring
:ExtractMethod(EM)-MoveMethod(MM)-DataObject(DO)-ExtractClass(EC)
EM MM DO EC
• Normalized Cohesion WB B B
• Non-normalized Cohesion WB B B
• General Coupling E B N S
• Export Coupling E B E E
• Aggregated import coupling B WWW
• Best, Worst, Expected, Suboptimal

29

Audits & Metric Links:
• Delphi XE Tool: Together

• http://www.modelmakertools.com/
• Report Pascal Analyzer:
http://www.softwareschule.ch/download/pascal_analyzer.pdf
• Refactoring Martin Fowler (1999, Addison-Wesley)
• http://c2.com/cgi/wiki?CodeSmell
• Model View in Together:
www.softwareschule.ch/download/delphi2007_modelview.pdf

30

Q&A
max@kleiner.com
www.softwareschule.ch

31

Metrics ekon 14_2_kleiner

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