Java

Which Java your game runs on, the experimental newer-Java switch, and when to touch the Java path setting.

Performance
Settings, Sour Client tab. The Java path is under Java runtime ; the per-profile Run on Java switch is on the Profiles page.
Settings, Sour Client tab. The Java path is under Java runtime; the per-profile Run on Java switch is on the Profiles page.

What it runs on

Forge 1.8.9 was built for Java 8, and that is what the launcher uses by default. It brings its own, so you never install Java yourself.

Run on Java 21

Open a 1.8.9 profile on the Profiles page and switch on Run on Java 21. On Java 8, the game usually stutters when it cleans up memory. On Java 21 those hitches mostly go away, and most PCs get more frames as well.

  • The first launch downloads Java 21 for you.
  • If the game crashes early on Java 21, the launcher switches the setting back off for that profile and tells you why, so the next launch starts on Java 8 as usual.
  • Turning the switch off puts everything back.
It is an experiment. A few older Forge mods do not run on Java 21; if one of yours does not, leave the switch off on that profile.

The Java path setting

Settings, Sour Client, Java runtime has a Java path. Leave it on the default (java): the launcher then picks the right bundled runtime for each version. Only change it if support asks you to. Reset puts it back.