I can see problems with your Venta class. You have lots of fields, but you do not initialise them in your constructor. You have a Scanner object, which you never use, so you might as well delete it.
You ought to provide a constructor which initialises the Venta object and getXXX methods which allow access to its fields.
You should find some similar examples
here. All the fields should have private access, so access can only be through the getXXX methods.
As for the output, Venta@17ce4e7, start reading
here.
why are you using Hashtable, which is legacy code? Why are you using
floats?