This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
The JVM needs some memory to do its work, and how much it uses is unspecified (and differs from one JVM version to the next). It depends on the implementation of the JVM. So your question can't be answered with a simple number.