Java time counting seconds in real time

You can use the Java service scheduler to display the times every second.

import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.concurrent.*;

public class Relogio {

    public static void main(String args[]) throws IOException {

        ScheduledExecutorService scheduler = Executors.newScheduledThreadPool(1);

        scheduler.scheduleAtFixedRate(
          new Runnable() {
              public void run() {
                  System.out.println(new SimpleDateFormat("HH:mm:ss").format(new Date()));
              }
        }, 1, 1, TimeUnit.SECONDS);
    }
}

There is no need to use the Thread class, nor use the sleep method, nor make any exception handling.

According to this answer in SO can do this:

import java.text.DateFormat;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class DateFormatExample {
    public static void main(String[] args) {
        Thread th = new Thread(new Runnable() { //cria uma thread
            public void run() {
                while(true) { //roda indefinidamente
                    Date date = Calendar.getInstance().getTime(); //pega a hora do sistema
                    DateFormat formatter = new SimpleDateFormat("HH:mm:ss");
                    String today = formatter.format(date);      
                    System.out.println(today);
                    try {
                        Thread.sleep(1000); //espera 1 segundo para fazer a nova evolução
                    } catch(InterruptedException ex){
                        //é algo terrível a se fazer mas pelo jeito a API medonha do Java exige
                    }
                }
            }
        });
        th.start();
    }
}

It may not give the best result but that's it. There are no guarantees that all screen updates will occur every 1 second accurate.

You have to position the cursor always in the same position but since I can not test, I'll just leave the code for you to try:

System.out.print(String.format("%c[%d;%df", 0x1B, 0, 0));

I think this is what you want

import java.text.SimpleDateFormat;
import java.util.Date;
import javax.swing.JLabel;

public class relogio {

    public static void main(String[] args) {
        try {  
            while (true) {  
                Date d = new Date();  
                StringBuffer data = new StringBuffer();  

                    SimpleDateFormat sdfData = new SimpleDateFormat("dd.MM.yyyy");  
                    data.append(sdfData.format(d));  
                    data.append(" - ");  

                SimpleDateFormat sdf = new SimpleDateFormat("HH:mm:ss");  
                System.out.println(""+data.toString() + sdf.format(d));

                Thread.sleep(1000);  
            }  
        } catch (InterruptedException ex) {  
            System.out.println("Problema na atualização da data/hora");  
            ex.printStackTrace();  
        }  
    }
}