Java9 or Java10 required to use Forge with 1.13/1.14 - but: installer has some issues to get https://launcher.mojang.com/v1/objects/d0d0fe2b1dc6ab4c65554cb734270872b72dadd6/server.jar as some wired quirk fails the crypto stuff. It works in Java8 and again in Java11/12. So, it's not cool force to use Java8 AND Java9/10 to let the installer run and run the game. By upgrade to ASM7.x Java11 could be used - solving that wired crypto issue. Also: Java11 is LTS - where as Java10 is already out of lifecycle.