public class Music {
  private static GreenfootSound track1, track2, track3;
  public Music() {
    track1 = new GreenfootSound("track1.mp3");
    track2 = new GreenfootSound("track2.mp3");
    track3 = new GreenfootSound("track3.mp3");
  }
  public static void stopAllTracks() {
    track1.stop();
    track2.stop();
    track3.stop();
  }
}

import greenfoot.*;
import java.util.*;

/**
 * Handles Sounds. Usage:
 * - fill the array soundNames with Strings (+ number them in comments)(
 * - enter a new line in the constructor with the according filename
 * 
 * Call from other classes
 * SoundHelper.playSound("EXPLOSION")
 * and
 * SoundHelper.stopSound("EXPLOSION");
 * also
 * SoundHelper.stopAllSounds();
 */
public class SoundHelper extends UIStuff
{
    private static boolean soundIsOn = true;
    private static String[] soundNames = {
            "EXPLOSION"     // 0
        ,   "SAD"  			// 1
        ,   "BGMUSIK"       // 2
        ,   "ACK"           // 3
        };
    static HashMap<String, GreenfootSound> soundMap = new HashMap<String, GreenfootSound>();

    public SoundHelper() {
        soundMap.put(soundNames[0], this.generateGFSound("explosion.wav"));
        soundMap.put(soundNames[1], this.generateGFSound("sad_sound.mp3"));
        soundMap.put(soundNames[2], this.generateGFSound("background_music.mp3"));
        soundMap.put(soundNames[3], this.generateGFSound("ack.mp3"));
    }

    private GreenfootSound generateGFSound (String soundfilename)
    {
        return new GreenfootSound(soundfilename);
    }

    static void playSound(String soundName) {
        if(SoundHelper.checkIfSoundExists(soundName)) { // array contains sound
            if(!SoundHelper.soundMap.get(soundName).isPlaying()) {
                SoundHelper.soundMap.get(soundName).play();
            }
        }
    }

    static void stopSound(String soundName) {
        if(SoundHelper.checkIfSoundExists(soundName)) { // array contains sound
            if(SoundHelper.soundMap.get(soundName).isPlaying()) {
                SoundHelper.soundMap.get(soundName).stop();
            }
        }
    }

    static void stopAllSounds() {
        for(String oneSoundName : SoundHelper.soundNames) {
            SoundHelper.stopSound(oneSoundName);
        }
    }
    static boolean checkIfSoundExists(String soundName) {
        for(String oneSoundName : SoundHelper.soundNames) {
            if(oneSoundName == soundName) {
                return true;
            }
        }
        System.out.println("ERROR - Sound " + soundName + " was called but doesn't exist. Check class SoundHelper.");

        return false;

    }

    static void toggleSound(boolean soundIsOn) {
        SoundHelper.soundIsOn = soundIsOn;
    }

}

import greenfoot.*;
import java.util.HashMap;
import java.util.Map;
 
/**
 * Handles Sounds. Usage:
 * 
 * Call from other classes
 *     Sound.play("explosion.wav")
 * and
 *     Sound.stop("explosion.wav");
 * or
 *     Sound.register("ACK", "ack.mp3");
 *     Sound.play("ACK");
 *     Sound.stop("ACK");
 * also
 *     Sound.stopAll();
 * also
 *     Sound.initializeDefaultSounds();
 *     Sound.play("SAD")
 */
public enum Sound
{
    ; // entry-less enum to prevent creation of any instances of static state class.

    private static boolean isOn = true; // TODO: Add functionality!
    private static final Map<String, GreenfootSound> sounds = new HashMap<>();

    public static void initializeDefaultSounds() { // not necessary
        register("EXPLOSION", "explosion.wav");
        register("SAD", "sad_sound.mp3");
        register("BGMUSIK", "background_music.mp3");
        register("ACK", "ack.mp3");
    }
 
    public static void register(final String fileName) {
        register(fileName, fileName);
    }
 
    public static void register(final String soundName, final String fileName) {
        final GreenfootSound alreadyRegisteredSound = sounds.get(soundName);
        if (alreadyRegisteredSound != null) {
            alreadyRegisteredSound.stop(); // make sure that old sound is stopped before replacing it.
        }
        sounds.put(soundName, create(fileName));
    }
 
    private static GreenfootSound create(final String fileName) {
        return new GreenfootSound(fileName);
    }
 
    public static void play(final String soundName) {
        final GreenfootSound sound = sounds.get(soundName);
        if (sound == null) { // register, if not yet existing.
            register(soundName);
        }
        if (!sound.isPlaying()) {
            sound.play();
        }
    }
 
    public static void stop(final String soundName) {
        final GreenfootSound sound = get(soundName);
        if (sound != null) {
            sound.stop();
        }
    }
 
    public static void stopAll() {
        for(final GreenfootSound sound : sounds.values()) {
            sound.stop();
        }
    }
    
    private static GreenfootSound get(final String soundName) {
        final GreenfootSound result = sounds.get(soundName);
        if (result == null) {
            System.out.println("ERROR - Sound " + soundName + " was called but doesn't exist. Check class SoundHelper.");
        }
        return result;
    }
 
    public static void toggleIsOn() {
        isOn = !isOn;
    }
 
}

Sound.play("SADD"); // instead of SAD

    public static void play(final String soundName) {
        final GreenfootSound sound = sounds.get(soundName);
        try {

            if (sound == null) { // register, if not yet existing.
                register(soundName);
            }
            if (!sound.isPlaying()) {
                sound.play();
            }
        } catch(Exception e) {
            System.out.println("Not existing sound has been called - not executed");           }
    }