I don't know exactly what time period you're referring to, but back when Java was attempting to take over the desktop UI world with Swing, it was painfully obvious when an app wasn't native on Windows. Eclipse was the first Java app I used that actually felt native, thanks to its use of native widgets (through a library called SWT) instead of Swing.
As far as I know, you can even write your own applications based on SWT which would make jvm apps pretty consistent and performant across platforms, but not many people seem to have chosen that route for some reason.
