Java - Check if JTextField is empty or not

For that you need to add change listener (a DocumentListener which reacts for change in the text) for your JTextField, and within actionPerformed(), you need to update the loginButton to enabled/disabled depending on the whether the JTextfield is empty or not.

Below is what I found from this thread.

yourJTextField.getDocument().addDocumentListener(new DocumentListener() {
  public void changedUpdate(DocumentEvent e) {
    changed();
  }
  public void removeUpdate(DocumentEvent e) {
    changed();
  }
  public void insertUpdate(DocumentEvent e) {
    changed();
  }

  public void changed() {
     if (yourJTextField.getText().equals("")){
       loginButton.setEnabled(false);
     }
     else {
       loginButton.setEnabled(true);
    }

  }
});

What you need is something called Document Listener. See How to Write a Document Listener.

To Check JTextFiled is empty or not condition:

if( (billnotf.getText().length()==0)||(billtabtf.getText().length()==0))

The following will return true if the JTextField name does not contain text:

name.getText().isEmpty();