Displaying changing values in JavaFx Label

Question

In JavaFX, how can I display values which continuously change with time using "label" ?

Answer 1

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();
    }
}

Answer 2

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:

Answer 3

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();
 }
}

Answer 4

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.