If running 0.48.0, update to 0.49.7.
Next, follow the instructions here EXACTLY, DO NOT SKIP ANY STEP AND READ OVER IT SEVERAL TIMES!!! (taken from the MM Discord where this question gets asked to the point we have a command for it).
If on 0.49.7, get Java 11. If on any version post 0.49.11, Can use 11 or 17.
** Java Update Protocol Activated!**
Hey MechWarriors! Time to power up your Java systems:
https://github.com/MegaMek/megamek/wiki/Updating-to-Adoptium:robot: **Critical Mission Briefing**:
1. Follow these steps **EXACTLY** – or risk facing the wrath of a misconfigured Mech!
2. Don't forget the **reboots** and **Step 6** – they're more important than a headshot with a PPC!
3. Current Java loadout: **Java 11 minimum, Java 17 maximum** (as of 0.49.11 Dev release, Dec 22, 2022).
4. Ignoring these steps might leave your Mech as useful as a Locust in an Atlas fight!
Remember, a well-updated Mech is a well-prepared Mech!