If they are executing using the same JVM: no. More likely though, you have three different JVMs running - so just use "top" (on Unix) or the Task Manager -> Processes window (Win NT/2000) to see all the processes running. Look for java processes (using the java executable in the JDK) and figure out which one is which. This may be done by starting / stopping some of the applications to see which lines of the output are affected - or using other clues which may be present. Once you identify the appropriate process, look at the column for memory usage. There you go. Offhand, I don't remember how/if you can do this on other Windows systems. Let us know what operating system you're using if you have further problems.
On Zin, you could use the Performance monitor, see here below :
Please note that the usage is not trivial to really understand what you see & how it affects your overall performances. Please note also that Linux VM has a bug with respect to the exact Memory used. It shows per thread the total memory used (AFAIK)instead of the memory used by the Thread (to verify)