How to install Java 21 for Minecraft 1.21.1 on Windows

Minecraft 1.21.1 runs on Java 21. Older Java versions can stop the game from starting. This guide shows how to check what you have and install the right one on Windows 10 or 11.

1. Check your current Java version#

Press the Windows key, type cmd and open Command Prompt. Type java -version and press Enter. If the first line shows a version that starts with 21, you are ready. If it shows 8, 11 or 17, or says Java is not recognised, continue.

2. Download Java 21#

Download a Java 21 build for Windows x64 from a trusted vendor. Eclipse Temurin and the Microsoft Build of OpenJDK are common choices. Pick the JDK or JRE 21 installer (.msi) and avoid unknown download sites.

3. Install it#

Run the installer. If it offers options such as adding Java to PATH or setting JAVA_HOME, enable them. Finish the install.

4. Check again#

Close Command Prompt, open a new one and run java -version. It should now show version 21.

5. Restart your launcher#

Close and reopen your launcher so it picks up the new Java. In FireClient, start the Minecraft 1.21.1 Fabric profile and check that it opens.

Common problems#

• Still shows an old version. Another Java install is earlier in your PATH. Uninstall the old one in Windows Settings, then check again.
• "Java not found". Reinstall and make sure the PATH option was enabled.
• Game still crashes. Follow the crash checklist.

Always download installers from the vendor's official site and never from a video description or file-sharing link. The safety guide explains how to verify a file with SHA-256.