Code Quality Metrics Demystified@JeroenResoort @jdriven_nl

What are metrics?

Why use metrics?

Why use metrics?To measure software quality

What is software quality?

Why use metrics?To measure and improve software maintainability attributes:

● Analysability

● Changeability

● Stability

● Testability

How to collect metrics?

How to use / collect metrics?IDE

CheckStyle

SonarQube

How to collect metrics?docker run -d --name sonarqube -p 9000:9000 -p 9092:9092 sonarqube

mvn sonar:sonar

Volume

VolumeFiles / Classes

Lines

Lines of code

LoC per file

LoC per method

Volumepublic int sum(int a, int b) {

return a + b;

}

Volumepublic int sumToo( int a

, int b )

{

int result = a + b;

return result;

}

Volumepublic List<Integer> calculate(List<Integer> numbers) {

return numbers.stream().map(i -> i * i).filter(i -> i % 2 == 0).collect(Collectors.toList());

}

Volumepublic List<Integer> calculateFormatted(List<Integer> numbers) {

return numbers.stream().

map(i -> i * i).

filter(i -> i % 2 == 0).

collect(Collectors.toList());

}

Volumeimport java.util.List;

import java.util.ArrayList;

import java.util.Set;

import java.util.HashSet;

Volumeimport java.util.*;

Cyclomatic Complexity

Cyclomatic ComplexityMcCabe, 1976

Control flow graph

Linearly independent paths

Cyclomatic Complexity

Cyclomatic ComplexityThe complexity M is defined as

M = E − N + 2P,

where

E = the number of edges of the graph.

N = the number of nodes of the graph.

P = the number of connected components.

Cyclomatic ComplexityAlternative formula

M = E − N + P

After connecting exit point to entry point

Cyclomatic Complexity

Cyclomatic Complexitypublic int sum(int a, int b) {

return a + b;

}

Cyclomatic Complexitypublic int sum(int[] amounts) {

int result = 0;

for (int i = 0; i < amounts.length; i++) {

result += amounts[i];

}

return result;

}

Cyclomatic Complexitypublic boolean checkWithdrawal(Account account, int amount) {

boolean result = false;if (account.getBalance() >= amount) {

result = true;}if (account.isLocked()) {

result = false;}return result;

}

Cyclomatic Complexitypublic boolean checkWithdrawal(Account acc, int amount) {

if (!acc.isLocked() && acc.getBalance() >= amount) {

return true;

}

return false;

}

Cyclomatic ComplexityComplexity per class

Complexity per method

Fan in / Fan out

Fan in / Fan outFan in: number of classes referencing you

Fan out: number classes you are referencing

Package Entanglement

Package Entanglement

Duplication

DuplicationHow to check?

Per line vs multiple lines?

Exact match or not?

Unit Test coverage

Unit Test coverageBad examples

Unit Test coverageAre your unit tests actually testing the right things?

Mutation tests!

ConclusionA lot of metrics available

Understand what they mean

Don’t use metrics as KPIs!

Questions?

Code Quailty Metrics Demystified@JeroenResoort @jdriven_nl