How to disable button when having 'some' text in a text field and re enabled them when that text disappears in the text field

Question

The situation is that the JButton1 corresponds to JLabel1, JButton2 to JLabel2 and so on. However I want to disable the JButton# when the value of Jlabel returns on the TextField and reenable them when it is gone.

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.*;
import javax.swing.*;

public class qwerty {

ArrayList<JTextField> tfs = new ArrayList<JTextField>();
ArrayList<JButton> bts = new ArrayList<JButton>();


int counter = 0;
String answer;
JLabel j1 = new JLabel("Mark");
JLabel j2 = new JLabel("Joe");
JLabel j3 = new JLabel("John");
JLabel j4 = new JLabel("Ray");

public static void main(String[] args) {
   EventQueue.invokeLater(new Runnable() {
        @Override
        public void run() {
            new qwerty();
        }
    });
}
 public qwerty() {

    JFrame frame = new JFrame();
    frame.getContentPane().setLayout(new FlowLayout());

    // Add new buttons to bts
    bts.add(new JButton("Button1"));
    bts.add(new JButton("Button2"));
    bts.add(new JButton("Button3"));
    bts.add(new JButton("Button4"));

   // Add new textfields to tfs
   tfs.add(new JTextField());
   tfs.add(new JTextField());
   tfs.add(new JTextField());



   j1.setPreferredSize(new Dimension(100, 25));
   j2.setPreferredSize(new Dimension(100, 25));
   j3.setPreferredSize(new Dimension(100, 25));
   j4.setPreferredSize(new Dimension(100, 25));


    for (JButton b : bts) {
        b.addActionListener(new ButtonActionListener());
        b.setPreferredSize(new Dimension(100, 25));
        frame.getContentPane().add(b);
    }

        frame.getContentPane().add(j1);
        frame.getContentPane().add(j2);
        frame.getContentPane().add(j3);
        frame.getContentPane().add(j4);



    for (JTextField tf : tfs) {
        tf.setPreferredSize(new Dimension(100, 25));
        tf.setEditable(false);
        frame.getContentPane().add(tf);
    }


    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(500, 500);
    frame.setVisible(true);

}

public class ButtonActionListener implements ActionListener {


    @Override
    public void actionPerformed(ActionEvent e) {
        if (counter >= tfs.size()) {
            counter = 0;
        }

        String a = ((AbstractButton) e.getSource()).getText();
        if (a == "Button1"){
        tfs.get(counter).setText(j1.getText());
        }   

        if (a == "Button2"){
        tfs.get(counter).setText(j2.getText());
        }

        if (a == "Button3"){
        tfs.get(counter).setText(j3.getText());
        } 

        if (a == "Button4"){
        tfs.get(counter).setText(j4.getText());
        } 

        counter++;
    }


}

}

Answer 1

import java.awt.*;
import java.awt.event.*;
import java.util.*;
import javax.swing.*;
import javax.swing.event.*;

public class qwerty implements DocumentListener{

ArrayList<JTextField> tfs = new ArrayList<JTextField>();
ArrayList<JButton> bts = new ArrayList<JButton>();


int counter = 0;
String answer;
JLabel j1 = new JLabel("Mark");
JLabel j2 = new JLabel("Joe");
JLabel j3 = new JLabel("John");
JLabel j4 = new JLabel("Ray");

JButton b1 = new JButton("Button1");
JButton b2 = new JButton("Button2");
JButton b3 = new JButton("Button3");
JButton b4 = new JButton("Button4");

public static void main(String[] args) {
   EventQueue.invokeLater(new Runnable() {
    @Override
    public void run() {
        new qwerty();
        }
    });
}
public qwerty() {

JFrame frame = new JFrame();
frame.getContentPane().setLayout(new FlowLayout());

// Add new buttons to bts
bts.add(b1);
bts.add(b2);
bts.add(b3);
bts.add(b4);

Add new textfields to tfs
tfs.add(new JTextField());
tfs.add(new JTextField());
tfs.add(new JTextField());



   j1.setPreferredSize(new Dimension(100, 25));
   j2.setPreferredSize(new Dimension(100, 25));
   j3.setPreferredSize(new Dimension(100, 25));
   j4.setPreferredSize(new Dimension(100, 25));


for (JButton b : bts) {
    b.addActionListener(new ButtonActionListener());
    b.setPreferredSize(new Dimension(100, 25));
    frame.getContentPane().add(b);
}

    frame.getContentPane().add(j1);
    frame.getContentPane().add(j2);
    frame.getContentPane().add(j3);
    frame.getContentPane().add(j4);



for (JTextField tf : tfs) {
    tf.setPreferredSize(new Dimension(100, 25));
    tf.setEditable(false);
    tf.getDocument().addDocumentListener( this );
    frame.getContentPane().add(tf);

}


frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(500, 500);
frame.setVisible(true);

}
        public boolean isDataEntered1()
    {

    for (JTextField tf : tfs)
    {

        if ("Mark".equals(tf.getText()))
            return false;
    }

    return true;
}

    public boolean isDataEntered2()
{

    for (JTextField tf : tfs)
    {

        if ("Joe".equals(tf.getText()))
            return false;
    }

    return true;
}

     public boolean isDataEntered3()
{

    for (JTextField tf : tfs)
    {

        if ("John".equals(tf.getText()))
            return false;
    }

    return true;
}

     public boolean isDataEntered4()
{

    for (JTextField tf : tfs)
    {

        if ("Ray".equals(tf.getText()))
            return false;
    }

    return true;
}


@Override
public void insertUpdate(DocumentEvent e) {
   checkData();
}

@Override
public void removeUpdate(DocumentEvent e) {
    checkData();
}

@Override
public void changedUpdate(DocumentEvent e) {}

private void checkData()
{
    b1.setEnabled(isDataEntered1());
    b2.setEnabled(isDataEntered2());
    b3.setEnabled(isDataEntered3());
    b4.setEnabled(isDataEntered4());
}

 public class ButtonActionListener implements ActionListener {


@Override
public void actionPerformed(ActionEvent e) {
    if (counter >= tfs.size()) {
        counter = 0;
    }

    String a = ((AbstractButton) e.getSource()).getText();
    if (a == "Button1"){
    tfs.get(counter).setText(j1.getText());
    }   

    if (a == "Button2"){
    tfs.get(counter).setText(j2.getText());
    }

    if (a == "Button3"){
    tfs.get(counter).setText(j3.getText());
    } 

    if (a == "Button4"){
    tfs.get(counter).setText(j4.getText());
    } 

    counter++;
}

} }