Well, that's cause the Java should be running a Java virtual machine to translate the Java executions into something that's windows-compatable. Thusly, java is a ram and processor hog, but it has the really nifty benefit of working on most every major platform out there with minimal alterations just being done to the GUI of the app.

45-80MB of RAM is basically inconsequential at 1GB of RAM, especially when you consider not only do you have that 1GB physical, but also basically unlimited virtual RAM.