running into 'incompatible error' message and casting will not solve

This is frustrating. If I cast, the error message 'incompatible error'
is replaced with another error message 'inconvertible error.' With just
using two class files, I am trying to learn how to do a formula in a
method file, then transfer the input into a variable within the main
class file. In the below coding, I am trying to figure out how to place
an object's data into a variable (or, as an alternative,
System.out.print the object data, but I run into errors when doing
that). Matter of fact, if I do not figure out this technique, I will
not be able to fully complete my school assignment. All 4 books I have
didn't even get me this far. Half of this stuff was trial an error.
Anyways, here is the coding from both files. Thank you for the help.

---CODING FOR MAIN CLASS FILE---

import java.io.*;

public class MainClass {

        public static void main(String[] args) throws IOException {

                //declare variables
                double jDouble = 0;
                BufferedReader dataIn = new BufferedReader(new
InputStreamReader(System.in));

                //object creation for input method
                InputMethod input = new InputMethod();

                jDouble = input.myInput();

                System.out.println(jDouble);

        }
}

---CODING FOR THE METHOD FILE---

import java.io.*;

public class InputMethod {

        String i;
        double iDouble;
        BufferedReader dataIn = new BufferedReader(new
InputStreamReader(System.in));

                //basic input method which converts a string into a
double
                public void myInput() throws IOException {
                        System.out.print("Enter some data: ");
                        i = dataIn.readLine();
                        iDouble = Double.parseDouble(i);
         }
 
}