title: Multiple textfields with one joptionpane
body: <p>I want a user to input 4 things (first name, last name, email and phone number) and in case he misses one or more just one <code>JOptionPane</code> window would show.</p>
  
  <pre><code> String firstname = TF_1.getText();
   String lastname = TF_2.getText();
   String email = TF_3.getText();
   String phonenumber = TF_4.getText();
  
  
   if (TF_1.equals("") ||
       TF_2.equals("") ||
       TF_3.equals("") ||
       TF_4.equals("")) {
  
   JOptionPane.showMessageDialog(null, "All text fields must be filled");
  </code></pre>