Sound, and the end of section 14.2

The last kind of multimedia in this module is sound: a click when a button is pressed, a chime when a message arrives, a cheer when a game is won.

Sound in JavaFX

JavaFX plays short sounds with the class AudioClip, from the package javafx.scene.media. On your own computer, a window with a button that plays a chime looks like this:

import java.nio.file.Paths;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.VBox;
import javafx.scene.media.AudioClip;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage stage) {
        AudioClip chime = new AudioClip(Paths.get("chime.wav").toUri().toString());
        Button ring = new Button("Ring the chime");
        ring.setOnAction(event -> chime.play());

        stage.setScene(new Scene(new VBox(ring)));
        stage.setTitle("Door chime");
        stage.show();
    }

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

• new AudioClip(...) takes the address of the sound file. Paths.get("chime.wav").toUri().toString() turns the file's name into its full address, which starts with file:, such as file:///home/ada/chime/chime.wav.
• The clip reads the whole sound when it's made, so play() starts at once. Calling play() again while it still plays starts the sound once more, over the first one.
• stop() stops it, setVolume(0.5) makes it play at half the volume (from 0.0 for silence to 1.0, the default), and setCycleCount(3) makes each play() play it three times in a row.
• For long sounds, such as music, JavaFX has Media and MediaPlayer, which play a file little by little instead of reading it all first.
• The sound classes are a part of JavaFX of their own, javafx.media, which a project needs next to the javafx.controls of the windows.

Sound in Java Arena

This page can't play sound. Java Arena's practice JavaFX has no javafx.scene.media, and the Java engine that runs your programs inside the page can't play sound. So here, javac stops at the import:

import javafx.scene.media.AudioClip;

public class Main {
    public static void main(String[] args) {
        AudioClip chime = new AudioClip("file:chime.wav");
        chime.play();
    }
}

Main.java:1: error: package javafx.scene.media does not exist
import javafx.scene.media.AudioClip;
                         ^
Main.java:5: error: cannot find symbol
        AudioClip chime = new AudioClip("file:chime.wav");
        ^
  symbol:   class AudioClip
  location: class Main
Main.java:5: error: cannot find symbol
        AudioClip chime = new AudioClip("file:chime.wav");
                              ^
  symbol:   class AudioClip
  location: class Main
3 errors

This step is for reading. The MOOC's exercise with sound, a button that plays a sound file, needs your own computer with JavaFX installed (module 48 links to the MOOC's instructions for that).

Deciding what to play

What a program decides about sound can still be written and checked here: which sound to play, and when. As in module 50, that decision goes in a plain class, and the window's handlers only carry it out. A quiz show's buzzer plays right.wav for a right answer and wrong.wav for a wrong one, except that the third wrong answer in a row plays out.wav and starts the count again. Here the handler prints the name of the clip where your computer would play it:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.control.Label;
import javafx.scene.layout.HBox;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class Main extends Application {

    @Override
    public void start(Stage stage) {
        Buzzer buzzer = new Buzzer();
        Label last = new Label("No answers yet");
        Button right = new Button("Right");
        Button wrong = new Button("Wrong");
        right.setOnAction(event -> {
            String clip = buzzer.clipFor(true);
            System.out.println("play " + clip);
            last.setText("Last sound: " + clip);
        });
        wrong.setOnAction(event -> {
            String clip = buzzer.clipFor(false);
            System.out.println("play " + clip);
            last.setText("Last sound: " + clip);
        });

        stage.setScene(new Scene(new VBox(10, new HBox(5, right, wrong), last)));
        stage.setTitle("Quiz buzzer");
        stage.show();
    }

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

public class Buzzer {
    private int wrongInARow;

    public String clipFor(boolean correct) {
        if (correct) {
            this.wrongInARow = 0;
            return "right.wav";
        }
        this.wrongInARow++;
        if (this.wrongInARow == 3) {
            this.wrongInARow = 0;
            return "out.wav";
        }
        return "wrong.wav";
    }
}

Window "Quiz buzzer"
  VBox spacing 10
    HBox spacing 5
      Button "Right"
      Button "Wrong"
    Label "Last sound: wrong.wav"

play wrong.wav
play wrong.wav
play right.wav
play wrong.wav

On your own computer, the handler would make an AudioClip for each of the three files in start, keep them in a map from the file's name to its clip, and call clips.get(clip).play() where this one prints. Buzzer stays the same, and every case of it can be tried by calling clipFor, with no sound at all.

Part 14 so far

Section 14.1 (module 51) and section 14.2 (this module) were about showing more than text:

• Charts (module 51): rows of data read from files into numbers, lists and maps; line charts with NumberAxis, XYChart.Series and XYChart.Data; several series from a map, and series from a formula; a Slider whose listener redraws a chart; bar charts with a CategoryAxis; and charts that are honest about their numbers.
• Drawing (steps 1 and 2): a Canvas and its GraphicsContext, with fill and stroke colors and a line width; rectangles, ovals given by the rectangle around them, lines and polygons, where later drawing covers earlier; colors by name, by Color.rgb and by Color.web; and the mouse, with its pressed, dragged, released and clicked events and the point in getX() and getY().
• Images (steps 3 to 6): an Image read from a file (or an error image when it can't be), its PixelReader, a WritableImage written through its PixelWriter, and an ImageView that shows it; smaller copies that keep every second (or every f-th) pixel; copies placed into bigger images; tiles with %, mirrored tiles; and filters: the negative, two kinds of gray, a threshold and tints.
• Sound (this step): AudioClip, for your own computer.

Section 14.3 builds a larger program with a window: a game in the style of Asteroids, with shapes that move and the keyboard to steer, in the next module.