JavaFX metronome with start/stop and tempo controls.

TickTock.java

import javafx.animation.Animation;
import javafx.animation.KeyFrame;
import javafx.animation.Timeline;
import javafx.application.Application;
import javafx.beans.binding.Bindings;
import javafx.beans.property.DoubleProperty;
import javafx.beans.property.ObjectProperty;
import javafx.beans.property.SimpleDoubleProperty;
import javafx.beans.property.SimpleObjectProperty;
import javafx.beans.value.ChangeListener;
import javafx.beans.value.ObservableValue;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.Slider;
import javafx.scene.control.ToggleButton;
import javafx.scene.image.Image;
import javafx.scene.layout.HBox;
import javafx.scene.media.AudioClip;
import javafx.scene.text.TextAlignment;
import javafx.stage.Stage;
import javafx.util.Duration;
import javafx.util.StringConverter;

import java.util.Date;

/** Creates a metronome with start/stop and tempo controls */
public class TickTock extends Application {
  private static final double INITIAL_TEMPO = 100;

  public static void main(String[] args) { launch(args); }

  @Override public void start(final Stage stage) {
    stage.setTitle("Metronome");
    stage.setScene(
        new Scene(
            new MetronomeView(new Metronome(INITIAL_TEMPO))
        )
    );
    stage.show();
  }
}

/** Provides a UI to control a metronome which ticks on pulses generated by a tempo in beats per minute. */
class MetronomeView extends HBox {
  private static final double MIN_TEMPO = 40;
  private static final double MAX_TEMPO = 180;

  public MetronomeView(Metronome metronome) {
    super(10);
    getChildren().addAll(
        createStartStopControl(metronome),
        createTempoControl(metronome),
        createTempoReadout(metronome)
    );
    setAlignment(Pos.CENTER);
    setStyle("-fx-background-color: cornsilk; -fx-padding: 10;");
  }

  protected Label createTempoReadout(Metronome metronome) {
    Label label = new Label();
    label.textProperty().bind(Bindings.format("%.0f", metronome.getPulsar().tempoProperty()));
    label.setPrefWidth(25);
    label.setAlignment(Pos.CENTER_RIGHT);

    return label;
  }

  protected Slider createTempoControl(Metronome metronome) {
    final Slider slider = new Slider(MIN_TEMPO, MAX_TEMPO, metronome.getPulsar().getTempo());
    slider.valueProperty().bindBidirectional(metronome.getPulsar().tempoProperty());
    slider.setMajorTickUnit(1);
    slider.setMinorTickCount(0);
    slider.setSnapToTicks(true);

    return slider;
  }

  protected ToggleButton createStartStopControl(final Metronome metronome) {
    final ToggleButton playControl = new ToggleButton("Start");
    playControl.setPrefWidth(60);
    playControl.selectedProperty().addListener(new ChangeListener<Boolean>() {
      @Override
      public void changed(ObservableValue<? extends Boolean> observableValue, Boolean wasSelected, Boolean selected) {
        if (selected) {
          metronome.getPulsar().start();
          playControl.setText("Stop");
        } else {
          metronome.getPulsar().stop();
          playControl.setText("Start");
        }
      }
    });
    return playControl;
  }
}

/** ticks according to a tempo in beats per minute controlled by the associated pulsar. */
class Metronome {
  private final AudioClip tick = new AudioClip("http://www.denhaku.com/r_box/sr16/sr16perc/losticks.wav");
  private final Pulsar pulsar;

  public Metronome(final double initialTempo) {
    // the first time the audioclip is played, there is a delay before you hear it,
    // so play with zero volume now as to make sure it is ready to play when straight away when needed.
    tick.play(0);

    pulsar = new Pulsar(initialTempo, new EventHandler<ActionEvent>() {
      @Override public void handle(ActionEvent actionEvent) {
        tick.play();
      }
    });
  }

  public Pulsar getPulsar() {
    return pulsar;
  }
}

/** handles events according to a tempo in beats per minute. */
class Pulsar {
  private final DoubleProperty tempo    = new SimpleDoubleProperty(100);
  private final Timeline       timeline = new Timeline();

  public Pulsar(final double initialTempo, final EventHandler<ActionEvent> pulseHandler) {
    timeline.setCycleCount(Animation.INDEFINITE);
    timeline.getKeyFrames().setAll(
        new KeyFrame(Duration.ZERO,       pulseHandler),
        new KeyFrame(Duration.minutes(1), null)
    );
    timeline.rateProperty().bind(tempo);

    setTempo(initialTempo);
  }

  public DoubleProperty tempoProperty() {
    return tempo;
  }

  public double getTempo() {
    return tempo.get();
  }

  public void setTempo(double newTempo) {
    tempo.set(newTempo);
  }

  public void start() {
    timeline.play();
  }

  public void stop() {
    timeline.stop();
  }
}