Code Help with GUI Mortgage Calculator

[drewdat7001]

Hello I'm trying to create a Mortgage Calculator that accepts user's input for loan amount, loan interest rate, and loan term and then displays the monthly payment for the Mortgage in GUI form. When I compile my program I get a error message stating cannot find symbol method showMessageDialog(<nulltype>,java.lang.String,int)

HERE IS MY CODE BELOW PLEASE HELP

import java.text.DecimalFormat;
import javax.swing.JOptionPane;

public class MortgageCalculatorServiceRequest4///Name of my File and Class
{
public static void main(String[] args)
{
double loanAmount;//Declaring my Variables
double loanInterest;//Declaring my Variables
double monthlyPayment;//Declaring my Variables
double interestRate;
int loanTerm;
String totalLoan, interestLoan, termLoan;
DecimalFormat decimalPlaces=new DecimalFormat("0.00"); //Format decimal point for proper display

totalLoan=JOptionPane.showInputDialog(null, "Enter the Term of the Loan: ");
loanAmount = Double.parseDouble(totalLoan);

interestLoan=JOptionPane.showInputDialog(null, "Enter the Interest Rate of the Loan in decimal Form: ");
loanInterest = Double.parseDouble(interestLoan)/12;

termLoan=JOptionPane.showInputDialog(null, "Enter the Term of the Loan: ");
loanTerm = Integer.parseInt(termLoan)*12;

// calculations
monthlyPayment = (loanAmount * loanInterest) / (1 - Math.pow(1 + loanInterest, -loanTerm));//Formula for Monthly Payments

JOptionPane.showMessageDialog(null,"Your Monthly Payments Are" + decimalPlaces.format(monthlyPayment),JOptionPane.PLAIN_MESSAGE );
System.exit(0);
}}