Allocating memory?

I'm making a mining game known as "Project Condor" (temporary name) link-http://greenfootgallery.org/scenarios/3319 When I'm programming i come across a problem that is kinda time consuming when i try to test just one little change in the code. Every time i compile the scenario in rapid succession i would keep getting an error message saying: I remember reading faintly that this is caused when the memory allocated to java becomes well full. and i wanted to know how to exactly increase the amount of memory java has access to so that it won't constantly become full. I tried looking at solutions and i found out that: java -Xms64m -Xmx256 (then program name) would do something like add a minimum of 64 megs and a max of 256 megs of memory to that programs available memory and i wanted to know how to make more memory in java available to Greenfoot so i can stop having "java heap space" error