Ajuda com MidiSystem

import java.io.File;
import java.io.IOException;
import javax.sound.midi.*;

public class Sons{
	private Sequence som;
	private Sequencer tocar;
	
	public void escolheMusica(String musica){
		final String sons = System.getProperty("user.dir")+"\sons\";
		try {
			this.som = MidiSystem.getSequence(new File(sons+musica+".mid"));
		} catch (InvalidMidiDataException e){
		} catch (IOException e){
		}
	}
	
	public void iniciar(){
		try {
			this.tocar = MidiSystem.getSequencer();
			this.tocar.open();
			this.tocar.setSequence(this.som);
			this.tocar.start();
    	} catch (MidiUnavailableException e){
    	} catch (InvalidMidiDataException e){
    	}
	}
	
	public void parar(){
		this.tocar.stop();
	}
}

...
	
	Sons musica = new Sons();

	musica.escolheMusica("abertura");
	musica.iniciar();

	...

	musica.parar();