Java Management

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How Polymerium Handles Java

Polymerium doesn't scan your system drive for Java installations. It uses two sources:

1. Manually configured Java — you specify a Java home directory.
2. Auto-deployed runtime — Polymerium downloads a matching Java runtime from Mojang into its cache.

When Auto-Deploy Happens

If you haven't configured a Java path (or the configured path doesn't work), Polymerium automatically downloads the appropriate runtime during deploy. This happens once — the runtime is cached and reused.

Auto-deployed runtimes live in cache/runtimes/ and don't touch your system registry or replace your system Java.

Supported Java Versions

Polymerium can manage multiple Java versions because different Minecraft versions require different JREs:

Configuring Java Paths

Go to Settings → Java to set Java home paths for each major version. Each field accepts a path to a JDK/JRE home directory (containing bin/java or bin/java.exe).

Per-Instance Override

You can override the Java version for a specific instance:

1. Open the instance's properties.
2. Set the Java home override to a specific path.

This is useful for testing compatibility or using optimized JVM distributions for specific instances.

Manual vs. Auto: Which to Use?

Troubleshooting Java Issues

• Wrong Java version → check the instance's Java override and the global Java settings for the matching version
• Java not found → remove the override and let auto-deploy fetch the right one
• Crash on launch → verify the Java path points to a valid JDK/JRE home (must contain bin/java)