Java Basics

A small Java 21 learning project that verifies my local Java toolchain and includes a command-line IPv4 subnet calculator.

This repository verifies that a Java 21 workflow works correctly with IntelliJ IDEA, Eclipse Temurin, Git, and GitHub on my Intel Mac setup.

Purpose

This is not intended to be a large Java application. It is a compact baseline project for:

• verifying the local Java toolchain
• practicing Java fundamentals
• testing IntelliJ IDEA with Eclipse Temurin 21 LTS
• keeping IDE metadata and build output out of Git
• maintaining a clean Git/GitHub workflow for Java projects

Java is a foundational programming skill in my current learning path. My main focus is data and process analysis, SQL, Python, BI, and Microsoft-oriented data tooling.

Tested Environment

• iMac Retina 4K, 21.5-inch, Late 2015
• Intel x86_64
• macOS Sonoma 14.8.7 via OpenCore Legacy Patcher
• IntelliJ IDEA via JetBrains Toolbox
• Eclipse Temurin 21 LTS
• Java 21
• Git / GitHub

This repository also documents that the Java 21 workflow works on a legacy Intel Mac setup used as a stable learning and development machine.

Repository Structure

java-basics/
├── src/
│   ├── HelloWorld.java
│   ├── Main.java
│   └── SubnetCalculator.java
├── .gitignore
├── LICENSE
└── README.md

Local IntelliJ IDEA files and build output are intentionally excluded from Git:

.idea/
out/
*.iml

Run in IntelliJ IDEA

Open the project in IntelliJ IDEA and run one of the following entry points:

• HelloWorld.main()
• Main.main()
• SubnetCalculator.main()

For SubnetCalculator.main(), use the following program argument:

192.168.10.42/24

Expected output:

Input IP:          192.168.10.42
CIDR prefix:       /24
Subnet mask:       255.255.255.0
Wildcard mask:     0.0.0.255
Network address:   192.168.10.0
Broadcast address: 192.168.10.255
Total addresses:   256
Usable hosts:      254
First usable host: 192.168.10.1
Last usable host:  192.168.10.254
Note:              Standard subnet with network and broadcast addresses excluded.

Run from Terminal

Compile the source files:

javac -d out src/*.java

Run HelloWorld:

java -cp out HelloWorld

Run the IPv4 subnet calculator:

java -cp out SubnetCalculator 192.168.10.42/24

Expected output:

Input IP:          192.168.10.42
CIDR prefix:       /24
Subnet mask:       255.255.255.0
Wildcard mask:     0.0.0.255
Network address:   192.168.10.0
Broadcast address: 192.168.10.255
Total addresses:   256
Usable hosts:      254
First usable host: 192.168.10.1
Last usable host:  192.168.10.254
Note:              Standard subnet with network and broadcast addresses excluded.

What This Demonstrates

This repository demonstrates a working Java 21 baseline setup using:

• Eclipse Temurin 21 LTS as the project JDK
• IntelliJ IDEA as the primary Java IDE
• a simple src/ based project structure
• a small command-line IPv4 subnet calculator
• Java records for structured result data
• IPv4 parsing and validation
• CIDR prefix handling
• subnet mask and wildcard mask calculation
• network and broadcast address calculation
• basic bitwise operations in Java
• local build output excluded from Git
• Git and GitHub for version control

Next Steps

Possible future additions:

• basic Java class and object examples
• additional small command-line exercises
• simple file input/output examples
• a small CSV parser
• basic unit tests later on

Notes

This repository is intentionally small. Its purpose is to document and verify a clean Java 21 development setup before building larger Java exercises or tools.

No IDE metadata, build output, or machine-specific files are committed.