Java - netbeans - Why is graphics rendering so slow.

[code_wrong]

I have written an app that processes images using netbeans.
When I run it from within Netbeans it seems to struggle to
draw the graphics in good time.

For example: I have a Jpanel on which I draw two BufferedImage
objects. Then I drag a red square around one of them.
There is a fair bit of processing going on as when I drag the
square, the image beneath it is set to it's red (rgb) parts only.
This means I need to draw BufferedImage then draw the square
with all the processing that that entails in a mousedrag method.
The square is only 100 pixels square.
The square lags behind the mouse badly.

I have also found that when rubber banding an object there is
an unacceptable lag.

Any ideas?
cheers
cw