How to pause all running threads? and then resume?

I have already seen this question : How pause and then resume a thread?

I have seen many questions in stackoverflow related to my issue, but I couldn't understand them because they are abstract and not specific enough to my sitiuation.

There are 2 Count Down Labels. When you click Start Button, the countdown is executed. In the same way, when you click Pause Button, it should be paused. However, I am getting an error: Exception in thread "AWT-EventQueue-0" java.lang.IllegalMonitorStateException

2 Threads are started, but I can't stop it with the wait() method. Please let me know how can I stop threads, and implement resume button. Thanks. Easy Example below

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

class FirstCountDown extends SwingWorker<Integer, Integer> {

public Integer doInBackground() {
    for(int i=0; i<1000; i++){
    CountDown.count1.setText(String.valueOf(1000-i));
    try {
        Thread.sleep(100);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    } 
    return null;
}
}

class SecondCountDown extends SwingWorker<Integer, Integer> {

public Integer doInBackground(){
    for(int i=0; i<1000; i++){
        CountDown.count2.setText(String.valueOf(1000-i));
    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    }
    return null;
}
}

class CountDown extends JFrame  {

static JLabel count1;
static JLabel count2; 
static JButton startButton;
static JButton pauseButton;
static JButton resumeButton;
FirstCountDown first = new FirstCountDown();
SecondCountDown second = new SecondCountDown();

public CountDown(){
count1 = new JLabel("1000");
count2 = new JLabel("1000");
startButton = new JButton("start");
startButton.addActionListener(new ActionListener()  {
    public void actionPerformed(ActionEvent e){
        first.execute();
        second.execute();
    }
});
pauseButton = new JButton("pause");
pauseButton.addActionListener(new ActionListener()  {
    public void actionPerformed(ActionEvent e){
        try {
            first.wait();
            second.wait();
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }
});

resumeButton = new JButton("resume");

setSize(300,100);
setLayout(new FlowLayout());
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
add(count1);
add(count2);
add(startButton);
add(pauseButton);
add(resumeButton);
setVisible(true);

        }

public static void main(String args[]) {

    CountDown g = new CountDown();

}
}