How to use switch Statement in Java?

import javax.swing.JOptionPane;
class cambien
{
  public static void main (String [] args)
  {
    String response;
    response = JOptionPane.showInputDialog
   ("what is your age?");
    if (response == null)
    {
      JOptionPane.showMessageDialog
        (null, "You clicked on the cancel button");
      System.exit (0);
    } //end of if satement
    
    else
      if (response.equals(""))
    {
    JOptionPane.showMessageDialog
      (null, " You must make an entry in the inputbox");
    System.exit (0);
    } // end of else if
    
    if(Integer.parseInt(response) > 25)
    {
      JOptionPane.showMessageDialog
        (null, response + " You must be Graduated");
      System.exit (0);
    }// end of if satement
    
    switch (Integer.parseInt(response)) 
    {
    case 22:
      JOptionPane.showMessageDialog
      (null, response + " You have 1 year untill Graduation");
      break;
    case 21:
      JOptionPane.showMessageDialog
      (null, response + " You have 2 years untill Graduation");
      break;
    case 20:
      JOptionPane.showMessageDialog
      (null, response + " You have 3 years untill Graduation");
      break; // end of case statements
    
    default:
      JOptionPane.showMessageDialog
    (null, response + " You have a long time untill you Graduate"); 
    }// end of switch stememnts
    System.exit (0);
    
  }// end of void main
}// end of cambien class