Activity Monitor shows java process, jps shows only JPS

MacVim forks (spawns a new process) to launch external processes, but it waits for the external process to return before resuming execution. Thus, killing MacVim simply detaches the child process (your program) from MacVim and attaches it to the main process running, in essence, OS X on the whole.

You have to quit, or Force Quit, your program explicitly in order to kill it.

It's also very likely that if you kill your program, and NOT MacVim, you can continue using MacVim without issue.

Check this out for a previous post. But, adding a bit to that answer...

First - while you have 4 physical cores, you have hyperthreading active, which allows each core to serve as 2 virtual cores. This will give you a theoretical maximum CPU usage of 100% x 8, or 800%.

Second - the % reported in the activity monitor is showing total CPU% (so it won't exceed 100%). Looking at the CPU numbers in your table, you're using a bit more than 485% out of the maximum of 800%. 485/800 is about 60%, which is your total usage reflected here...