两数求和java（字符串强转int型）

import javax.swing.JOptionPane;

public class Addition {    public static void main( String args[] )    {      

                             String firstNumber,secondNumber;     

                            int number1, number2, sum;           

                            firstNumber =JOptionPane.showInputDialog( "Enter first integer" );

                            secondNumber = JOptionPane.showInputDialog( "Enter second integer" );

                            number1 = Integer.parseInt( firstNumber );      

                           number2 = Integer.parseInt( secondNumber );

                           sum = number1 + number2;

                          JOptionPane.showMessageDialog(          null, "The sum is " + sum, "Results",          JOptionPane.PLAIN_MESSAGE );

                          System.exit( 0 );    

}

}