Clase Mostardor

import java.util.LinkedList;

public class Mostrador<T> {

    private LinkedList<Integer> bizcochos = new LinkedList<>();
    private LinkedList<Integer> facturas = new LinkedList<>();

    public Mostrador() {

    }

    public synchronized boolean noHayBizc() {
        if (bizcochos.size()<=0) return true;
        notifyAll();
        return false;
    }

    public synchronized boolean noHayFact() {
        if (facturas.size()<=0) return true;
        notifyAll();
        return false;
    }

    public synchronized void agregarBizcocho(int elemento) {
         bizcochos.addLast(elemento);
         notifyAll();
    }

    public synchronized void agregarFactura(int elemento) {
        facturas.addLast(elemento);
        notifyAll();
    }

    public synchronized int comprarBizcocho() {
        while(bizcochos.size()<=0) {
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
          int elemento = bizcochos.removeFirst();
          notifyAll();
          return elemento;
    }

    public synchronized int comprarFactura() {
        while(facturas.size()<=0) {
            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
          int elemento = facturas.removeFirst();
          notifyAll();
          return elemento;
    }
}