You can't just "shut down Java", and it's probably the application and not Java itself that's using all that memory.
If you don't need Java for anything you're doing on purpose, you might be able to sniff out who's using it by uninstalling it and seeing who complains.
How, exactly, did you decide that "Java" was using 1GB of memory? If you';re looking at the "Processes" tab on Windows Task Manager, for example, you can switch over to the applications tab, right click on one of them and choose "Go to Process" to see what main program that's running "java" or "javaw". I get under 100KB usage running GeoGebra 5, for example, and that's the running application *plus* the Java virtual machine combined.
If you're still stumped, the SysInternals Process Explorer can help. That's a set of free add-on tools developed by Mark Russinovich and later bought by Microsoft.
https://docs.microsoft.com/en-us/sysinternals/