How to disable button in Java until all fields filled

[1144999]

Hi I'm new to Java and developing a small school project. I'm making a program where the user has to register themselves. I have 3 different tabs on my Tabbed Pane. I want to be able to disable the "next button" on the first pane making it impossible for the user to continue to pane 2 unless all the text fields on pane 1 have been filled. I have been researching online and found various examples however none would work in run time.

I am using Netbeans.

private void txtFirstNameActionPerformed(java.awt.event.ActionEvent evt) {                                             
 
    if(txtFirstName.getText().trim().length() > 0)
 
        btnNext1.setEnabled(true);
    else 
        btnNext1.setEnabled(false); 
  }
 

[chaarmann]

You can check after every key-press (and/or pasting), that means after every text change, if all input fields of the pane are filled. If yes, enable the "next"-button. But if there exists at least one field that is empty, disable the button.