A simple java program, showing how to play a tune.

Synth.java

import java.util.Arrays;
import java.util.List;

import javax.sound.midi.MidiSystem;
import javax.sound.midi.Synthesizer;
import javax.sound.midi.MidiChannel;

/**
 * A little example showing how to play a tune in Java.
 * 
 * Inputs are not sanitized or checked, this is just to show how simple it is.
 * 
 * @author Peter
 */
public class Synth {
	
	private static List<String> notes = Arrays.asList("C", "C#", "D", "D#", "E", "F", "F#", "G", "G#", "A", "A#", "B");
	private static MidiChannel[] channels;
	private static int INSTRUMENT = 0; // 0 is a piano, 9 is percussion, other channels are for other instruments
	private static int VOLUME = 80; // between 0 et 127
	
	public static void main( String[] args ) {
		
		try {
			// * Open a synthesizer
			Synthesizer synth = MidiSystem.getSynthesizer();
			synth.open();
			channels = synth.getChannels();

			// * Play some notes
			play("6D",  1000);
			rest(500);
			
			play("6D",  300);
			play("6C#", 300);
			play("6D",  1000);
			rest(500);
			
			play("6D",  300);
			play("6C#", 300);
			play("6D",  1000);
			play("6E",  300);
			play("6E",  600);
			play("6G",  300);
			play("6G",  600);
			rest(500);
			
			// * finish up
			synth.close();
		}
		catch (Exception e) {
			throw new RuntimeException(e);
		}
	}
	
	/**
	 * Plays the given note for the given duration
	 */
	private static void play(String note, int duration) throws InterruptedException
	{
			// * start playing a note
			channels[INSTRUMENT].noteOn(id(note), VOLUME );
			// * wait
			Thread.sleep( duration );
			// * stop playing a note
			channels[INSTRUMENT].noteOff(id(note));
	}
	
	/**
	 * Plays nothing for the given duration
	 */
	private static void rest(int duration) throws InterruptedException
	{
		Thread.sleep(duration);
	}
	
	/**
	 * Returns the MIDI id for a given note: eg. 4C -> 60
	 * @return
	 */
	private static int id(String note)
	{
		int octave = Integer.parseInt(note.substring(0, 1));
		return notes.indexOf(note.substring(1)) + 12 * octave + 12;	
	}
}

cool, it even works :P

Do I have permission to use some of this code to help someone in a Bounty on Replit? I will credit you of course.

Sure, go for it. The above is hereby released under an MIT license.

Ok, thank you so much!

Playing is cool. But can we write this to a file like wav instead of playing it?

Capturing audio is described in the docs here https://docs.oracle.com/javase/tutorial/sound/capturing.html It seems a bit more involved. maybe stackexchange has some ready-to-use code.

Thanks!