Code metrics

Code quality

© 2012 Cognifide Limited. In commercial confidence only.

What is code quality
• Sample code quality questions:
− Are methods and classes clean, readable and short?
− Are connections between classes well-designed?
− Does your code follow Java conventions?


private static final rather than private final static

− Do you have unit tests? What is the coverage?
− Don’t you have some other code-smells?


Eg. if statement with too many || conditions

• Some issues caused by low quality code:
−
−
−
−

Problems with adding new features
Problems with collaboration
Hidden bugs
Hard to debug

• Static code analysis tools can check all things automatically
• Sonar – popular tool for Java


Coding standards


Coding standards – example
class FileUtils {
public final static String pngExtension = "png";
public static String getExtension(String filename) {
int DOTPos = filename.indexOf(".");
if (filename != null && DOTPos > -1) {
String extension = filename.substring(DOTPos+1);
return extension;
}
return null;
}
}


Cyclomatic complexity


Cyclomatic complexity
•
•
•
•
•

Basic code metric
Describes number of “branches” in method or class
Sequential code (no ifs, fors and whiles): complexity = 1
Each additional condition: +1
If method is too complex, we should split it into smaller ones


House of cards


Complexity for sequential code
byte[] buffer = new byte[1024];
InputStream stream = new FileInputStream("/my/file");
InputStream buffered = new BufferedInputStream(stream);
buffered.read(buffer);
buffered.close();

• Complexity: 1
• No conditions, simple flow


Complexity with one condition
byte[] buffer = new byte[1024];
File file = new File("/my/file");
if (!file.exists()) {
return;
}
InputStream stream = new FileInputStream(file);
InputStream buffered = new BufferedInputStream(stream);
buffered.read(buffer);
buffered.close();

• Complexity: 2


Complexity: formal definition
Formal definition: Edges – Nodes + 2 Components
for(int i=0;i<3;i++) {
System.out.println(i);
}

if(j == 42) {
System.out.println(”j is the answer”)
}
Edges: 9, Nodes: 8, Components: 1
E-N+2P=3


Class responsibilities


Single responsibility principle
• Each class should be responsible for only one thing
• Example: class Driver:
− 2 fields: car, brain,
− 5 methods: drive(), goTo(), stop(), getAngry(), drinkCoffee(),

• This class has 3 responsibilities:
− Driving car
− Getting angry
− Drinking coffe

• It should be split into 3 classes


LCOM4 & cohesion
• LCOM4 – Lack Of Cohesion Methods.
• How many responsibilities class?
• LCOM4 = 3 means that
− there are 3 not connected sets of methods/properties
− class can be split into three new classes.

• Class should be designed to have LCOM4 = 1
• Low LCOM4 = high cohesion
• Cohesion relates to coupling


Coupling


Tight coupling
• If a class (eg. Driver) invokes methods on some other class
(eg. Car) it’s tightly coupled with it
• In this case we can’t easily change Car implementation to
something other (eg. Tank)
• Real-life example: iPhone and its battery
public class Driver {
private final Car car;
public Driver(Car car) {
this.car = car;
}
public void driveCar() {
car.startEngine();
car.drive();
}

public class Car {
public void startEngine() {
…
}
public void drive() {
…
}
}

}

Loose coupling
• Class doesn’t need to know about other classes existence
• It only need to know about contracts (interfaces) provided by
other class
• Real-life example: screw and screwdriver
public class Driver {
private Vehicle vehicle;
public Driver(Vehicle vehicle) {
this.vehicle = vehicle;
}
vehicle.startEngine();
vehicle.drive();
}

public interface Vehicle {
void startEngine();
void drive();
}
public class Car implements Vehicle {
public void startEngine() {
…
}
…
}

}
}


Coupling & cohesion – summary
• Classes must be loosely coupled
and highly cohesive.
• Cohesion is the degree to which the
methods of a single class are tight
together.
− If class is not cohesive (eg. two methods
doesn’t share any property), it can be
split to two classes.

• Coupling is the degree to which each
class is tight to the others.
− Any change you make in one class has
impact to some other classes.
− Use interfaces & depdency injection

• Read more…
• Read even more…


Technical debt


Technical debt
• „Doing things the quick and dirty way sets us up with a
technical debt, which is similar to a financial debt.”
• Metric based on:
−
−
−
−
−

•
•
•
•

duplications,
violations,
(lack of) comments,
coverage,
complexity.

Absolute debt in mandays and cash
Debt ratio – dependent on the project size.
Useful for project manager
Read more...


Other metrics


Other code metrics
•
•
•
•
•

Lines of code
Unit test coverage
Responses for class
…
All these metrics can be checked via Sonar
− Free & very useful software
− Can be integrated with Eclipse

• Visual Studio provides integrated metrics as well


Code metrics

Recommended

Recommended

More Related Content

What's hot

What's hot (14)

Viewers also liked

Viewers also liked (17)

Similar to Code metrics

Similar to Code metrics (20)

More from Tomasz Rękawek

More from Tomasz Rękawek (7)

Recently uploaded

Recently uploaded (20)

Code metrics