jvm design decision

Question

Why does the jvm require around 10 MB of memory for a simple hello world but the clr doesn't. What is the trade-off here, i.e. what does the jvm gain by doing this?

Let me clarify a bit because I'm not conveying the question that is in my head. There is clearly an architectural difference between the jvm and clr runtimes. The jvm has a significantly higher memory footprint than the clr. I'm assuming there is some benefit to this overhead otherwise why would it exist. I'm asking what the trade-offs are in these two designs. What benefit does the jvm gain from it's memory overhead?

Answer 1

I guess one reason is that Java has to do everything itself (another aspect of platform independence). For instance, Swing draws it's own components from scratch, it doesn't rely on the OS to draw them. That's all got to take place in memory. Lots of stuff that windows may do, but linux does not (or does differently) has to be fully contained in Java so that it works the same on both.

Java also always insists that it's entire library is "Linked" and available. Since it doesn't use DLLs (they wouldn't be available on every platform), everything has to be loaded and tracked by java.

Java even does a lot of it's own floating point since the FPUs often give different results which has been deemed unacceptable.

So if you think about all the stuff C# can delegate to the OS it's tied to vs all the stuff Java has to do for the OS to compensate for others, the difference should be expected.

I've run java apps on 2 embedded platforms now. One was a spectrum analyzer where it actually drew the traces, the other is set-top cable boxes.

In both cases, this minimum memory footprint hasn't been an issue--there HAVE been Java specific issues, that just hasn't been one. The number of objects instantiated and Swing painting speed were bigger issues in these cases.