Java Swing memory usage

Question

There are plenty of questions on this issue, but no answer satisfied me; I'm coding a simple GUI window using Swing. Currently it only contains 4 buttons and one of them is opening a file chooser.

When I use VisualVM Monitoring tool to look at memory usage, the result is shown below:

memory usage http://img17.imageshack.us/img17/3589/8txc.png

The first pike appeared when I clicked the button, then I did nothing else.

Is this normal for an idle application to consume 10M/min (when it is not doing anything?)

Since I have to do a quizz-like applet with an image, should I use to call System.gc() each time I switch to the next question to avoid (potentially huge?) memory usage?

Answer 1

I could recreate what you saw with a simple test program, but if you let the monitor track a little longer...

CPU was at 0% the whole time (just an open JFileChooser sitting there). The memory fluctuations are curious, but I think the JVM must be doing all kinds of background management and maintenance tasks. That work will use memory which eventually builds up. And periodically it cleans up after itself.

Another thing to consider is that is this memory usage within the already allocated heap. Your program is actually using a consistent amount of real memory the entire time, as you can see from the flat orange line.