โค้ตการคำนวณดอกเบี้ยเงินฝาก ด้วยโปรแกรมจาวาค่ะ

นี่คือโค้ตที่เขียนค่ะ ลองรันก้อขึ้นนะค่ะ แต่พอกดปุ่มคำนวณกลับขึ้น error เยอะมากเลยค่ะ ไม่รุ้ว่าโค้ตผิดตรงไหน ช่วยดูให้หน่อยนะค่ะ
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;

class NaijinSaejao extends Frame implements WindowListener,ActionListener
{
    Label    lblMoney, lblInterest;
    TextField    txtMoney, txtInterest;
    Button    bCalc, bExit;

    NaijinSaejao()
    {
        super("Naijin Saejao IT56.1 NO.25");
        this.addWindowListener(this);
        GridLayout G = new GridLayout(3,2);
        this.setLayout(G);
        this.setSize(300,300);
        this.setResizable(true);

        lblMoney = new Label("เงินฝาก    :");
        txtMoney = new TextField(20);
        lblInterest = new Label("ดอกเบี้ย    :");
        txtInterest = new TextField(20);
        txtInterest.setEnabled(false);

        bCalc = new Button("Calulator");
        bCalc.addActionListener(this);
        bExit = new Button("Exit");
        bExit.addActionListener(this);

        add(lblMoney);            add(txtMoney);
        add(lblInterest);        add(txtInterest);
        add(bCalc);                add(bExit);
        this.setVisible(true);
    }
    //---------------------------------------------------------------------

    public void windowClosing(WindowEvent W)
    {
        System.exit(0);
    }
    public void windowClosed(WindowEvent W){}
    public void windowOpened(WindowEvent W){}
    public void windowActivated(WindowEvent W){}
    public void windowDeactivated(WindowEvent W){}
    public void windowIconified(WindowEvent W){}
    public void windowDeiconified(WindowEvent W){}
    //---------------------------------------------------------------------

    public void actionPerformed(ActionEvent A)
    {
        if (A.getSource()==bCalc)
        {
            calInt();
        }
        if (A.getSource()==bExit)
        {
            System.exit(0);
        }
    }//end actionPerformed
    //---------------------------------------------------------------------


    private void calInt()
    {
        double mon,my;
        double i = Double.parseDouble(txtInterest.getText());
        my=i/12;
        if (i<=100)
        {
            mon = i*0.002;
            txtMoney.setText(String.valueOf(mon));
        }
        else if (i<=1000)
        {
            mon = i*0.003;
            txtMoney.setText(String.valueOf(mon));
        }
        else if (i<=10000)
        {
            mon = i*0.005;
            txtMoney.setText(String.valueOf(mon));
        }
        else
        {
            mon = i*0.10;
            txtMoney.setText(String.valueOf(mon));
        }
        
    }//end calDb
//------------------------------------------------------------------------

    public static void main(String[] args)
    {
        NaijinSaejao N = new NaijinSaejao();
    }
}