Installing Java on Windows — OpenJDK 21 Setup Guide

In this chapter, you’ll install the Java Development Kit (JDK) 21 on Windows. We’ll cover two methods — the graphical installer and the command-line approach — and verify everything works.

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Method 1: Install Using Adoptium (Recommended)

Eclipse Adoptium provides free, production-ready OpenJDK builds called Eclipse Temurin.

Step 1: Download the Installer

1. Go to https://adoptium.net/
2. The site auto-detects your OS — click “Latest LTS Release” (Java 21)
3. Download the .msi installer for Windows x64

Step 2: Run the Installer

1. Double-click the downloaded .msi file
2. Click Next through the wizard
3. Important: Check these options when they appear:
   • ✅ Set JAVA_HOME variable
   • ✅ Add to PATH
4. Click Install and wait for completion

Step 3: Verify Installation

Open PowerShell (press Win + X, select “Windows PowerShell”) and run:

$ java -version

Expected output:

openjdk version "21.0.2" 2024-01-16 LTS
OpenJDK Runtime Environment Temurin-21.0.2+13 (build 21.0.2+13-LTS)
OpenJDK 64-Bit Server VM Temurin-21.0.2+13 (build 21.0.2+13-LTS, mixed mode, sharing)

$ javac -version

Expected output:

javac 21.0.2

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Method 2: Install Using winget (Command Line)

If you prefer the command line, winget (Windows Package Manager) makes installation easy:

$ winget install Microsoft.OpenJDK.21

Or for Eclipse Temurin:

$ winget install EclipseAdoptium.Temurin.21.JDK

After installation, close and reopen PowerShell, then verify:

$ java -version
$ javac -version

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Setting JAVA_HOME Manually

If the installer didn’t set JAVA_HOME automatically:

Step 1: Find the JDK Installation Path

The default location is usually:

C:\Program Files\Eclipse Adoptium\jdk-21.0.2+13

Or for Microsoft OpenJDK:

C:\Program Files\Microsoft\jdk-21.0.2.13-hotspot

Step 2: Set JAVA_HOME in Environment Variables

1. Press Win + S and search for “Environment Variables”
2. Click “Edit the system environment variables”
3. Click “Environment Variables…“ button
4. Under System variables, click New:
   • Variable name: JAVA_HOME
   • Variable value: C:\Program Files\Eclipse Adoptium\jdk-21.0.2+13 (your actual path)
5. Find the Path variable under System variables, click Edit
6. Click New and add: %JAVA_HOME%\bin
7. Click OK on all dialogs

Step 3: Verify

Close and reopen PowerShell:

$ echo $env:JAVA_HOME
C:\Program Files\Eclipse Adoptium\jdk-21.0.2+13

$ java -version
openjdk version "21.0.2"

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Test with Hello World

Create a folder for your Java projects and test:

$ mkdir $HOME\java-projects
$ cd $HOME\java-projects

Create a file called HelloWorld.java (use Notepad or any text editor):

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, World! Java is working on Windows!");
    }
}

Compile and run:

$ javac HelloWorld.java
$ java HelloWorld

Expected output:

Hello, World! Java is working on Windows!

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Common Issues and Fixes

Problem	Solution
'java' is not recognized	Close and reopen PowerShell. If still failing, add JDK bin folder to PATH manually
'javac' is not recognized	You have JRE, not JDK. Reinstall with JDK
Wrong version showing	Check PATH order — the first java.exe found wins. Remove old Java from PATH
UAC blocks installer	Right-click installer → “Run as administrator”

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Summary

Step	Action
Download	adoptium.net → Java 21 LTS → Windows .msi
Install	Run installer, check “Set JAVA_HOME” and “Add to PATH”
Verify	java -version and javac -version in PowerShell
Test	Compile and run HelloWorld.java

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What’s Next?

• Choosing an Editor or IDE →