ClassObjects

A simple Java project demonstrating object-oriented programming concepts with classes and objects. This project includes a Student class implementation and UML diagrams to visualize the class structure.

Project Overview

This project demonstrates how to:

• Create and use Java classes
• Implement object instances
• Model real-world entities as code
• Visualize class structures with PlantUML

Java Classes and Objects

What are Classes and Objects?

In Java, a class is a blueprint or template that defines the properties (attributes) and behaviors (methods) that objects of that class will have. An object is an instance of a class.

Think of a class as a cookie cutter, and objects as the cookies made from it - each cookie has the same shape but can have different decorations or flavors.

Key Concepts

• Class: The template that defines attributes and methods
• Object: An instance of a class
• Attributes: Variables that store data about the object
• Methods: Functions that define the behavior of the object
• Constructor: Special method to initialize new objects
• Encapsulation: Hiding internal state through private variables and public methods

Using Classes and Objects in Java

1. Define a class:

public class Student {
    private int age;
    private String name;
    
    // Constructor
    public Student(int age, String name) {
        this.age = age;
        this.name = name;
    }
    
    // Methods
    public void setAge(int age) {
        this.age = age;
    }
    
    public void setName(String name) {
        this.name = name;
    }
}

2. Create objects (instances):

Student max = new Student(20, "Max Mustermann");
Student hannah = new Student(21, "Hannah Mustermann");

3. Access methods and properties:

max.setAge(22);
hannah.setName("Hannah Schmidt");

PlantUML

PlantUML is an open-source tool that allows you to create UML diagrams from a simple text language.

Installation

1. Prerequisites:

   • Java Runtime Environment (JRE)
   • Graphviz (for some diagram types)

2. Installation options:

   • Download standalone JAR from PlantUML website
   • Install via package managers:
     • macOS: brew install plantuml
     • Linux: apt-get install plantuml (Debian/Ubuntu)
   • Use as a plugin in IDEs:
     • IntelliJ IDEA (PlantUML integration plugin)
     • Visual Studio Code (PlantUML extension)
     • Eclipse (PlantUML plugin)

How to Use PlantUML

1. Create a .puml file with your diagram definition:

@startuml Class_Example
class Student {
  - age: int
  - name: String
  + Student(int age, String name): void
  + setAge(int age): void
  + setName(String name): void
}
@enduml

2. Generate the diagram:

   • Command line: java -jar plantuml.jar file.puml
   • IDE: Use the plugin's preview or export functions
   • Online: Use the PlantUML web server

3. PlantUML Syntax:

   • Class members:
     • + public
     • - private
     • # protected
   • Relationships:
     • -- association
     • <|-- inheritance
     • *-- composition
     • o-- aggregation

For more details, visit the PlantUML website.

Code Formatting in VS Code

Visual Studio Code offers powerful code formatting capabilities to keep your Java code clean and consistent.

Setting Up Java Formatter

1. Install Java Extension Pack:

   • Open VS Code
   • Go to Extensions (Ctrl+Shift+X or Cmd+Shift+X on macOS)
   • Search for "Java Extension Pack" and install it

2. Configure Formatter Settings:

   • Open Settings (Ctrl+, or Cmd+, on macOS)
   • Search for "java format"
   • Customize settings like tab size, indentation, and line wrapping

3. Format Options:

   • Format current file: Right-click and select "Format Document" or use Shift+Alt+F (Windows/Linux) or Shift+Option+F (macOS)
   • Format selection: Select code, right-click and choose "Format Selection" or use Ctrl+K Ctrl+F (Windows/Linux) or Cmd+K Cmd+F (macOS)
   • Format on save: Enable "Editor: Format On Save" in Settings

4. Configure Java-specific formatting rules:

   • Create a formatter profile XML file:
     • Export from Eclipse or download a template
     • In VS Code settings, set "java.format.settings.url" to the path of your XML file

5. Keyboard Shortcuts for Formatting:

   • Format document: Shift+Alt+F (Windows/Linux) or Shift+Option+F (macOS)
   • Format selection: Ctrl+K Ctrl+F (Windows/Linux) or Cmd+K Cmd+F (macOS)

Consistent formatting helps maintain code readability and makes collaboration easier across development teams.