Many java.exe processes after finish working with Intellij

It could be silly question but I wanna figure out in my mind whats going on. I am testing web applications with tomcat in the Intellij and after all there are a lot of java.exe process in the task manager.

So, my questions are:

  1. Why do they still eat my memory and not terminated after closing all programs e.g Intellij? Is this a tricks from JVM?
  2. How elegant or correct should i close it?