Is there a plugin that allows you to type 'immediate' java commands?

e.g., a plugin with a single-line text field, when you press enter it
compiles it into a default file with default imports etc., and gives
you a result that you can store in a temporary variable.

I was thinking it would be soooo useful for debugging - e.g. you could
'test out' a single line of code. Or issue immediate commands like

'a = new JFrame()'  <ENTER>

then

'a.show()' <ENTER>

If not, then would anyone else find such a thing useful?

Sanjay