Programa de adição

import javax.swing.JOptionPane;  

public class Addition {
    
        public static void main(String args[]) {
        
        String firstNumber,
        secondNumber;           
        int number1;  
        int number2;                  
        int sum;                        
                
           firstNumber =
           JOptionPane.showInputDialog("Enter first integer");
        
           secondNumber =
           JOptionPane.showInputDialog("Enter secong integer");
        
         number1 = Integer.parseInt(firstNumber);
         number2 = Integer.parseInt(secondNumber);
        
         sum = number1 + number2;
        
                JOptionPane.showMessageDialog(null,"The sum is", + sum, "Results",              // está dando erro aqui!
                JOptionPane.PLAIN_MESSAGE);
        
        System.exit(0);           
    }
}