Apache Maven

Distribution Intermezzo

What does it take to build, distribute & run java application?

What are the distribution options?

What is Maven

• From Yiddish word meaning “Expert”
• Originally developed to simplify build of Jakarta Turbine
• A tool used to build and manage Java-based projects
• Currently in version 3.9.x
• Apache Maven

Maven’s Goals

1. Making the build process eas(y/ier)
2. Providing a uniform build system
3. Providing quality project information
4. Encouraging better development practices

Maven What?

1. Describes how to build your project via POM file descriptor
2. Allows you to define useful metadata about your project
3. Provides dependency management
4. There are reasonable defaults

Project structure

project_root
|- src
    |- main
        |- java
        |- resources
    |- test
        |- java
        |- resources
|- pom.xml

Project Object Model

• Project descriptor named pom.xml
• Each project identified by GAV

<project>
    <modelVersion>4.0.0</modelVersion>

    <groupId>cz.muni.fi.pv168</groupId>
    <artifactId>zinger</artifactId>
    <version>1.0-SNAPSHOT</version>
</project>

Maven Dependencies

• Maven projects can be published to repositories
• Default remote repository is Maven Central
• Ability to use multiple repositories
• Local repository in ${M2_HOME}/repository typically ~/.m2/repository on Unix systems

POM Example

Let’s look at full pom.xml

• What dependencies does this project have?
• What is the build output?
• What metadata does the project provide?

Maven Alternatives

“I don’t like it, what are the other options?”

• Though luck, you need it!
• There is one, Gradle
• You still need to know Maven!

PV168

The Calculator Application

Back to the original version

• Where the code does come from?
  • It is an example from GeeksForGeeks website on how to use Java Swing
• What was wrong with it?
• How would you call these problems in the code?
  • The industry standard term is Code Smell

Now to the reworked version

• What was better in this reworked version?
• How did it happen that we have it?
• How would you call these transformations of the code?
  • The industry standard term is Refactoring

Code Smells vs. Refactoring

• A little bit of medical analogies
  • Code Smell tells us what the code suffers from (diagnosis)
  • Refactoring describes how we can cure it (therapy)
• Where do these terms come from?

Recommended reading

Refactoring: Improving the Design of Existing Code, 2^nd edition

Martin Fowler, Kent Beck

Addison-Wesley Professional, 2019

https://www.amazon.com/gp/product/B07LCM8RG2

Code Smells in the original version

• Mysterious Name
• Long Function
• Duplicated Code
• Comments

• Find out more about Code Smells at Refactoring Guru
  • https://refactoring.guru/refactoring/smells

The Most Usefull Refactorings

• Rename
• Extract Method
• Extract Variable
• Inline

• Find out more about Refactorings at Refactoring Guru
  • https://refactoring.guru/refactoring/techniques

What is Refactoring

• Refactoring (noun): a change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior.

  (Martin Fowler, Refactoring, page 45)

• Refactoring (verb): to restructure software by applying a series of refactorings without changing its observable behavior.

  (Martin Fowler, Refactoring, page 45)

What is not Refactoring

• If someone says their code was broken for a couple of days while they are refactoring, you can be pretty sure they were not refactoring.

  (Martin Fowler, Refactoring, page 45)

Key Requirement

• Before you start refactoring, make sure you have a solid suite of tests.

  (Martin Fowler, Refactoring, page 5)

Test Categories

• End-to-End
  • Testing the whole system, starting at the GUI down to the persistence
  • Automating them is out of scope of PV168
• Integration
  • Testing collaboration of multiple components
• Unit
  • Testing a single unit (in isolation)

Usability Problems in the Calculator

• There were many of them
• But the most prominent was …
  • The layout