How to constantly validate a JTextField?

Question

I have a Java application that has a form with 4 text fields and a button. I was wondering if there is a way for the program to be constantly checking the fields using .isEmpty() to see if there has been an input yet, and once there is an input in all fields, the button will become available to click?

Answer 1

Add a DocumentListener.

        JButton button = new JButton("Button");
        JTextField field = new JTextField();
        field.getDocument().addDocumentListener(new DocumentListener(){

            @Override
            public void changedUpdate(DocumentEvent arg0) {
                if(field.getText().isEmpty()){
                    button.setEnabled(true);
                }
            }

            @Override
            public void insertUpdate(DocumentEvent arg0) {
                if(field.getText().isEmpty()){
                    button.setEnabled(true);
                }
            }

            @Override
            public void removeUpdate(DocumentEvent arg0) {
                if(field.getText().isEmpty()){
                    button.setEnabled(true);
                }
            }

        });