Chapter 4: How to Install Java?

OpenJDK (Open Java Development Kit) is a free and open-source implementation of the Java programming language. It is widely used for development and production environments.

This guide provides step-by-step instructions to install OpenJDK on Windows, Linux, and macOS.

Install OpenJDK on Windows

Step 1: Download OpenJDK

1. Visit the OpenJDK download page: - https://jdk.java.net (Official OpenJDK builds)
- Alternatively, use https://adoptium.net (Eclipse Temurin)

2. Select the latest JDK version for Windows.

3. Download the .zip file (no installer required).

Step 2: Extract OpenJDK

1. Extract the downloaded .zip file to a preferred directory (e.g., C:\Java\).

2. Rename the folder to a shorter name, e.g., C:\Java\jdk-XX.

Step 3: Set Up Java Environment Variables

To run Java globally, set the JAVA_HOME and Path variables.

1. Open Environment Variables:
- Press Win + R, type sysdm.cpl, and hit Enter.
- Go to the Advanced tab → Click Environment Variables.

2. Set JAVA_HOME:
- Click New under System Variables.
- Variable Name: JAVA_HOME
- Variable Value: C:\Java\jdk-XX (your OpenJDK path).
- Click OK.

3. Add Java to PATH:
- Select Path under System Variables, click Edit → New.
- Add: C:\Java\jdk-XX\bin.
- Click OK → Restart your computer.

Step 4: Verify Java Installation

Open Command Prompt (cmd) and run:

java -version
javac -version

If Java is installed correctly, it will display the version details.



Install OpenJDK on Linux

Step 1: Update System Packages

Before installing Java, update the package repository:

sudo apt update && sudo apt upgrade  # Ubuntu/Debian
sudo dnf update                      # Fedora
sudo yum update                      # CentOS



Step 2: Install OpenJDK

Ubuntu/Debian-based distributions:

sudo apt install openjdk-XX-jdk


Example: Installing OpenJDK 21:

sudo apt install openjdk-21-jdk


Fedora:

sudo dnf install java-XX-openjdk


CentOS/RHEL:

sudo yum install java-XX-openjdk


Replace XX with the required version (e.g., 21 for Java 21).




Step 3: Set JAVA_HOME (Optional)

To set the Java environment variable:



1. Find the Java installation path:

sudo update-alternatives --config java


Example output:

/usr/lib/jvm/java-21-openjdk-amd64/bin/java


2. Open the .bashrc or .profile file:

nano ~/.bashrc


or 

nano ~/.profile


3. Add the following lines at the end:

export JAVA_HOME=/usr/lib/jvm/java-21-openjdk-amd64
export PATH=$JAVA_HOME/bin:$PATH


4. Save and exit (CTRL + X, then Y and Enter).

5. Apply the changes:

source ~/.bashrc


Step 4: Verify Java Installation

Run the following command:

java -version
javac -version

This should display the installed Java version.

Install OpenJDK on macOS

Step 1: Check If Java Is Installed

macOS may come with an older version of Java. Check with:

java -version

If Java is not found, proceed with installation.

Step 2: Install OpenJDK Using Homebrew (Recommended)

Homebrew is a package manager for macOS. Install OpenJDK with:

brew install openjdk

To install a specific Java version (e.g., Java 21):

brew install openjdk@21

Step 3: Set JAVA_HOME (Optional)

1. Open Terminal.
2. Edit the shell configuration file:

nano ~/.zshrc  # For macOS Catalina and later

or

nano ~/.bash_profile  # For older macOS versions

3. Add the following lines:

export JAVA_HOME=$(/usr/libexec/java_home)
export PATH=$JAVA_HOME/bin:$PATH

4. Save and exit (CTRL + X, then Y and Enter).
5. Apply the changes:

source ~/.zshrc

or

source ~/.bash_profile

Step 4: Verify Java Installation

Check if Java is installed correctly:

java -version
javac -version