import javax.swing.*;

import java.lang.*;

public class Addtion

{

public static void main(String[] args)

{

String FirstNumber,SecondNumber,Result;

int number1,number2,sum;

FirstNumber = JOptionPane.showInputDialog("Enter first number:");

SecondNumber = JOptionPane.showInputDialog("Enter second number:");

number1 = Integer.parseInt(FirstNumber);

number2 = Integer.parseInt(SecondNumber);

sum = number1+number2;

JOptionPane.showMessageDialog("The sum is:"+sum);

System.exit(0);

}

}

当运行的时候，系统总是报错：（如图）

请问这是怎么回事啊？？？？？？？？？？？