How to see Javadoc documentation on mouse hover in NetBeans?

You can view the javadoc in Netbeans by clicking on the method and press Ctrl + Shift + Space
(Command + Shift + Space on Mac) You can also see the various shortkeys in the help menu>keyboard shortcuts card.

UPDATE:

You can instead open a "javadoc" window from the menu Window>IDE Tools>Javadoc Documentation. This will show the javadoc in a window near the output window for that method when you click on the method or object

I know that in netbeans 8.0 you can hold down the ctrl button and hover over the class or method, etc. and the javadoc window would appear.

Javadoc won't show up with just a mouse hover, but you can click on a word (method/class/field/variable/whatever name) and press ctrl+space. Javadoc should show up.

You can even open Javadoc window and you can see the javadoc in that. I prefer this way

Window >> Other >> javadoc.

Now you can see both your code and respective javadoc.

Update for Netbeans 8:

Window >> IDE Tools >> Javadoc Documentation