ButtonHAndler.java

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.concurrent.*;
import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import javax.swing.JButton;
import javax.swing.JOptionPane;
import java.lang.*;

public class ButtonHandler implements ActionListener {
private JButton iniciar, parar, resetar;

ScheduledFuture<?> result;

int counter = 0;

boolean isAlive = false;

public ButtonHandler(JButton iniciar, JButton parar, JButton resetar){
        this.iniciar = iniciar;
        this.parar = parar;
        this.resetar = resetar;
}

public void actionPerformed(ActionEvent evento) {
        if(evento.getSource() == iniciar) {

                if (isAlive != true ) {
                        initCounter();
                        isAlive = true;
                }
                else {System.out.println("Ele já está rodando"); }
        }

        if (evento.getSource() == parar) {
                if (isAlive == true) {
                        stopCounter();
                        isAlive = false;
                }
        }

        if (evento.getSource() == resetar) {
                if (isAlive == true) {
                        resetCounter();
                }
                else {
                        resetCounter2();
                }
        }
}

public void initCounter() {
        Runnable runnable = new Runnable() {
                @Override
                public void run() {
                        incrementCounter();
                        System.out.println(counter);
                }
        };

        ScheduledExecutorService service = Executors.newSingleThreadScheduledExecutor();
        result = service.scheduleWithFixedDelay(runnable, 0, 1, TimeUnit.SECONDS);
}

public void stopCounter() {
        result.cancel(true);
        System.out.println("Contador parado em " + counter);
}

public void resetCounter() {
        result.cancel(true);
        System.out.println("Contador resetado em " + counter);
        counter = 0;

        initCounter();
}

public void resetCounter2() {
        result.cancel(true);
        System.out.println("Contador resetado em " + counter);
        counter = 0;
}

public void incrementCounter() {
        counter++;
}
}