Temperature Conversion Project - Send Input Value To Calculation Area And Get Value To Display In JLabel

The problem I'm trying to resolve now is getting my ActionEvent to send the value input in the JTextArea out to be calculated, then to display the result in my result JLabel.

Here is an image of the GUI :

The basic procedure the teacher is asking for is the user is supposed to enter a temperature in the input. The user then clicks the input scale, and then on the output scale selection the converted value is to be displayed in the output area.

As I mentioned my problem is in the sending of the input value to my calculation area, and getting the value to display in the JLabel.

How should I approach this solution? Do I need to have a listener after the JTextArea of the input box? Will that allow me to limit the input values to numbers only?

final JTextArea inputText = new JTextArea("" + (char)176,1,4);
//ReadConsole equivalent to specific input was a number?

Here is the section of code my ActionListener is:

//celOut represents the Celcius output scale JRadioButton.
celOut.addActionListener (new ActionListener () {

@Override
public void actionPerformed(ActionEvent e) {
//if the Celcius Input Scale is selected.
if(cel.isSelected())

[Code] ....

All the calculations are required to occur in a separate java file, which what I think is tripping me up. How do I send a value from the JTextArea into the Calc.celToFahr method?

//contents of my Calc.java calculation class.
public class Calc {
public static double celToFahr(double cel){
return cel * (9./5.) + 32.;
}
public static double fahrToCel(double fahr){
return (fahr - 32.)*(5./9.);
}
}