How to use if statement to check for empty input box in java?

import javax.swing.JOptionPane; //imports swing class
class Practice
{
  public static void main (String [] args)
  {
    String response; //creates "respose" string
    response = JOptionPane.showInputDialog //assignment of response 
      ("what is your first name?");
    if (response == null) 
      JOptionPane.showMessageDialog
      (null, "You clicked on the cancel button");
    else
    if (response.equals(""))
      JOptionPane.showMessageDialog
      (null, "You must make an entry in the input box");
    else
      JOptionPane.showMessageDialog
      (null," It's nice to meet you " + response);
    System.exit (0);
  }
}// end of Practice