Please help me with my GUI!

Guys please help me on my program, this is a GUI java program, and I'm having problem every time I run it. It doesn't give me any output on every given I enter, it got an error always. This is a Confidence Interval of know variance, that's the title of my program.. I want it to give me an output every time I press the calculate button. Here's the code..
Code Java:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class MyProgram2 extends JFrame implements ActionListener{
    JLabel heading = new JLabel("Given:");
    JLabel sSize = new JLabel("Sample Size");
    JLabel sMean = new JLabel("Sample Mean");
    JLabel var = new JLabel("Variance"); 
    JLabel ConfInt = new JLabel("Confidence Interval");
    JLabel ans = new JLabel("Two sided");
 
    JTextField textA = new JTextField(7);
    JTextField textB = new JTextField(7);
    JTextField textC = new JTextField(7);
    JTextField textD = new JTextField(7);
    JTextField textE = new JTextField(7);
    JTextField textF = new JTextField(7);
    JTextField ConfInttext = new JTextField(7);
    JTextField resultA = new JTextField(7);
    JTextField resultB = new JTextField(7);
 
    JButton calculate = new JButton("Calculate");
 
    JPanel hedpanel = new JPanel();
    JPanel row1 = new JPanel();
    JPanel row2 = new JPanel();
    JPanel row3 = new JPanel();
    JPanel row4 = new JPanel();
    JPanel result = new JPanel();
    JPanel butpanel = new JPanel();
    double a;
    double b; 
    double c;
    double d;
    double e; 
    double f; 
    double g; 
    double finalans; 
    double h;
    double i; 
    double j;
    double k;
    double l;
    double m;
    double n;
    double finalans2;
 
    public MyProgram2(){
        setTitle("Confidence Interval of two Population Mean");
        resultA.setEditable(false);
        resultB.setEditable(false);
        setLayout(new FlowLayout());
 
        //Add component to Panel
 
        hedpanel.add(heading);
 
        row1.add(sSize);
        row1.add(textA);
        row1.add(textB);
 
        row2.add(sMean);
        row2.add(textC);
        row2.add(textD);
 
        row3.add(var);
        row3.add(textE);
        row3.add(textF);
        row4.add(ConfInt);
        row4.add(ConfInttext);
 
        result.add(ans);
        result.add(resultA);
        result.add(resultB);
 
        butpanel.add(calculate);
 
        //Frame
        add(hedpanel);
        add(row1);
        add(row2);
        add(row3);
        add(row4);
        add(result);
        add(calculate);      
 
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        calculate.addActionListener(this);
    }
        //the Application
        public void calcCIL(){
            finalans = (c-d)-g*Math.sqrt((Math.pow(e,2)/a)+(Math.pow(f,2)/b));
        }
        public void calcCIR(){
            finalans2 = (j-k)+n*Math.sqrt((Math.pow(l,2)/h)+(Math.pow(m,2)/i));
        }
        public void actionPerformed(ActionEvent evt){
            String userIn;
            userIn = textA.getText();
            a = Integer.parseInt(userIn);
            h = Integer.parseInt(userIn);
 
            userIn = textB.getText();
            b = Integer.parseInt(userIn);
            i = Integer.parseInt(userIn);
 
            userIn = textC.getText();
            c = Integer.parseInt(userIn);
            j = Integer.parseInt(userIn);
 
            userIn = textD.getText();
            d = Integer.parseInt(userIn);
            k = Integer.parseInt(userIn);
 
            userIn = textE.getText();
            e = Integer.parseInt(userIn);
            l = Integer.parseInt(userIn);
 
            userIn = textF.getText();
            f = Integer.parseInt(userIn);
            m = Integer.parseInt(userIn);
 
            userIn = ConfInt.getText();
            g = Integer.parseInt(userIn);
            n = Integer.parseInt(userIn);
 
            resultA.setText(finalans+"");
            repaint();
            calcCIL();
            resultB.setText(finalans2+"");
            repaint();
            calcCIR();
 
        }
        public static void main(String[] args){
            MyProgram2 prog = new MyProgram2();
            prog.setSize(350, 290);
            prog.setResizable(false);
            prog.setVisible(true);
 
        }
}