New to Java

This is a question i saw in a mock exam.


You are concerned about that your program may attempt to use more memory than is
available. To avoid this situation you want to ensure that the Java Virtual Machine will
run its garbage collection just before you start a complex routine. What can you do to
be certain that garbage collection will run when you want.
(1) You cannot be certain when garbage collection will run
(2) Use the Runtime.gc() method to force garbage collection
(3) Ensure that all the variables you require to be garbage collected are set to null
(4) Use the System.gc() method to force garbage collection


Now,as far as my little knowledge in java,GC manages the available memory and doesnot CREATE more memory for my program to run.So what is the highlighted part trying to suggest ?

1. Also is my assumption correct ?
2. How do i know how much memory is allocated in my machine for my JVM ?
3. Is memory space in JVM and the heap space in memory for the objects one and the same ?


I hope my questions make sense,and i am just too confused reading various terminologies on memory management.

Thank you for your consideration.