JAVA代码正确，为何运行错误.请各位大侠解救

import javax.swing.*;
public class AverageNumbers
{
public static void main (String [] args)
{
String s1,info,outMessage;

final int MAXNUMS = 4;
int count;
double num,total,average;

outMessage = "This program will ask you to enter" + MAXNUMS + "numbers.";
JOptionPane.showInternalMessageDialog(null, outMessage,"Program 5.7",JOptionPane.INFORMATION_MESSAGE);

count = 1;
total = 0;

while (count <= MAXNUMS)
{
s1 = JOptionPane.showInputDialog("Enter number " + count +":");
num = Double.parseDouble(s1);

total = total + num;
outMessage = outMessage + num + "";
count++;
}

average = total / MAXNUMS;
JOptionPane.showMessageDialog(null,outMessage + "\nis" + average,"Pragrame 5.7",JOptionPane.INFORMATION_MESSAGE);