Clase Factura

import java.util.Random;
import javax.lang.model.element.Element;

public class Factura extends Thread{

    private static int contador = 0;
    private int indice;
    private Mostrador<Element> cola;
    private Random random = new Random();
    private int lim_superior = 1300;
    private int lim_inferior = 1000;

    public Factura(Mostrador<Element> mostrador) {
        contador++;
        this.indice = contador;
        this.cola = mostrador;
    }

    public void run() {
        while (true) {
            // System.out.println((cola.toString()));
            int elemento = this.indice;
            cola.agregarFactura(elemento);
            System.out.println("Factura " + this.indice +" se añadió al mostrador");
            try {
                Thread.sleep(random.nextInt(this.lim_inferior, this.lim_superior));
            } catch (InterruptedException e) {
                Thread.currentThread().interrupt();
            }
        }
    }
}