If you want to write an interactive terminal / console based application in Java (perhaps on a headless server) then Lanterna (a Google Code project) makes this very easy.
Download the Lanterna jar from http://code.google.com/p/lanterna/ and here is a simple example to get you started:
import com.googlecode.lanterna.*;
import com.googlecode.lanterna.terminal.*;
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;

public class Term
{
   private Terminal term;
   private DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

   public Term()
   {
       term = TerminalFacade.createTerminal();

       term.enterPrivateMode();

       while (true)
       {
           term.clearScreen();

           String dateString = df.format(new Date());
           term.applySGR(Terminal.SGR.ENTER_BOLD);
           term.applyForegroundColor(Terminal.Color.RED);

           show(dateString, 0, 0);

           term.flush();

           try
           {
               Thread.sleep(1000);
           }
           catch (InterruptedException ie)
           {
               ie.printStackTrace();
           }
       }
   }

   private void show(String str, int x, int y)
   {
       term.moveCursor(x, y);

       int len = str.length();

       for (int i = 0; i < len; i++)
       {
           term.putCharacter(str.charAt(i));
       }
   }

   public static void main(String[] args)
   {
       new Term();
   }
}
Build on the command line using:
javac -cp lanterna-2.0.4.jar Term.java
Run on the command line using:
java -cp lanterna-2.0.4.jar Term