It looks like you declared reference (which by the way is a  terrible name for a variable) of type JTextField in the class Save, but you never initialized it. That is why you are getting a NullPointerException.

You new it in the Constructor class. 

After you have newed the JTextField in the constructor class, you need to pass the JTextField variable as an argument to either the constructor of the Save class, or to a method of the Save the class, and use that to get the text from the text field.

Also, you don't want to call toString on the JTextField. toString will not get you the data in the textfield. You want getText().

Java - Not being able to get data from Text Field
Hi I am designing a 6A current source. I know how to design a current source I am just looking for suggested materials that can handle the full 6A. The op amps and transistors that I have now are more on the milliamp side so I just am looking for something beefier.
