Displaying changing values in JavaFx Label

There are numerous ways to achieve that, the most convenient would be to use JavaFX's DataBinding mechanism:

// assuming you have defined a StringProperty called "valueProperty"
Label myLabel = new Label("Start");
myLabel.textProperty().bind(valueProperty);

This way, every time your valueProperty gets changed by calling it's set method, the label's text is updated.

How about using SimpleDateFormat? There's no need for the StringUtilities class!

private void bindToTime() {
  Timeline timeline = new Timeline(
    new KeyFrame(Duration.seconds(0),
      new EventHandler<ActionEvent>() {
        @Override public void handle(ActionEvent actionEvent) {
          Calendar time = Calendar.getInstance();
          SimpleDateFormat simpleDateFormat = new SimpleDateFormat("HH:mm:ss");
          setText(simpleDateFormat.format(time.getTime()));
        }
      }
    ),
    new KeyFrame(Duration.seconds(1))
  );
  timeline.setCycleCount(Animation.INDEFINITE);
  timeline.play();
 }
}

I like Sebastian's binding answer.

For variety, here is another sample of modifying a label text based upon time. The sample displays a digital clock readout in a label whose text changes each second using an Timeline.

import java.io.IOException;
import java.net.URL;
import javafx.animation.*;
import javafx.event.*;
import javafx.scene.control.Label;
import javafx.util.Duration;

import java.util.Calendar;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.stage.Stage;

public class DigitalClockSample extends Application {
  public static void main(String[] args) { launch(args); }
  @Override public void start(Stage stage) throws IOException {
    stage.setScene(new Scene(new DigitalClock(), 100, 50));
    stage.show();
  }
}

/**
 * Creates a digital clock display as a simple label.
 * Format of the clock display is hh:mm:ss aa, where:
 * hh Hour in am/pm (1-12)
 * mm Minute in hour
 * ss Second in minute
 * aa Am/pm marker
 * Time is the system time for the local timezone.
 */
class DigitalClock extends Label {
  public DigitalClock() {
    bindToTime();
  }

  // the digital clock updates once a second.
  private void bindToTime() {
    Timeline timeline = new Timeline(
      new KeyFrame(Duration.seconds(0),
        new EventHandler<ActionEvent>() {
          @Override public void handle(ActionEvent actionEvent) {
            Calendar time = Calendar.getInstance();
            String hourString = StringUtilities.pad(2, ' ', time.get(Calendar.HOUR) == 0 ? "12" : time.get(Calendar.HOUR) + "");
            String minuteString = StringUtilities.pad(2, '0', time.get(Calendar.MINUTE) + "");
            String secondString = StringUtilities.pad(2, '0', time.get(Calendar.SECOND) + "");
            String ampmString = time.get(Calendar.AM_PM) == Calendar.AM ? "AM" : "PM";
            setText(hourString + ":" + minuteString + ":" + secondString + " " + ampmString);
          }
        }
      ),
      new KeyFrame(Duration.seconds(1))
    );
    timeline.setCycleCount(Animation.INDEFINITE);
    timeline.play();
  }
}

class StringUtilities {
  /**
   * Creates a string left padded to the specified width with the supplied padding character.
   * @param fieldWidth the length of the resultant padded string.
   * @param padChar a character to use for padding the string.
   * @param s the string to be padded.
   * @return the padded string.
   */
  public static String pad(int fieldWidth, char padChar, String s) {
    StringBuilder sb = new StringBuilder();
    for (int i = s.length(); i < fieldWidth; i++) {
      sb.append(padChar);
    }
    sb.append(s);

    return sb.toString();
  }
}

Digital clock sample output:

Excellent responses, thank you jewelsea for your input it helped me a lot.

I updated the DigitalClock posted previously in a leaner format using Java 8. Using the additions of Java 8 like Date API and of course the lambdas.

 import javafx.animation.Animation;
 import javafx.animation.KeyFrame;
 import javafx.animation.Timeline;
 import javafx.scene.control.Label;
 import javafx.util.Duration;

 import java.time.LocalTime;
 import java.time.format.DateTimeFormatter;

 public class DigitalClock extends Label
 {
    private static DateTimeFormatter SHORT_TIME_FORMATTER =       DateTimeFormatter.ofPattern("HH:mm:ss");

    public DigitalClock()
    {
        bindToTime();
    }

    private void bindToTime() {
        Timeline timeline = new Timeline(new KeyFrame(Duration.seconds(0),
                                                      event -> setText(LocalTime.now().format(SHORT_TIME_FORMATTER))),
                                         new KeyFrame(Duration.seconds(1)));

        timeline.setCycleCount(Animation.INDEFINITE);
        timeline.play();
    }
}