The program stops when it arrives at .wait ()

The thing is that the execution of the threads of my program stops when it reaches the wait (), having a notify () after ...

package supermercado;

import static java.lang.Thread.sleep;
import java.util.ArrayList;
import java.util.Scanner;
import java.util.logging.Level;
import java.util.logging.Logger;


public class Supermercado {

    static float ingresos;
    static ArrayList<Cliente> arrClientes = new ArrayList<Cliente>();
    static ArrayList<Caja> arrCajas = new ArrayList<Caja>();
    static ArrayList<Thread> arrTClientes = new ArrayList<Thread>();
    static ArrayList<Thread> arrTCajas = new ArrayList<Thread>();

    public Supermercado() {
        Scanner sc;
        int n1 = 0, n2 = 0;
        do {
            try {
                sc = new Scanner(System.in);
                System.out.println("Introduce cantidad de clientes:");
                n1 = sc.nextInt();
            } catch (Exception ex) {
                System.out.println("Formato incorrecto");
                n1 = 0;
            }
        } while (n1 <= 0);
        do {
            try {
                sc = new Scanner(System.in);
                System.out.println("Introduce cantidad de cajas:");
                n2 = sc.nextInt();
            } catch (Exception ex) {
                System.out.println("Formato incorrecto");
                n2 = 0;
            }
        } while (n2 <= 0);
        for (int i = 0; i < n1; i++) {
            Cliente c = new Cliente();
            arrClientes.add(c);
            arrTClientes.add(new Thread(c));
        }
        for (int i = 0; i < n2; i++) {
            Caja c = new Caja();
            arrCajas.add(c);
            arrTCajas.add(new Thread(c));
        }
        for (int i = 0; i < arrTClientes.size(); i++) {
            arrTClientes.get(i).start();
        }
        try {
            sleep(200);
        } catch (InterruptedException ex) {
            Logger.getLogger(Supermercado.class.getName()).log(Level.SEVERE, null, ex);
        }
        for (int i = 0; i < arrTCajas.size(); i++) {
            synchronized (arrCajas) {
                //arrCajas.get(i).notifyAll();
            }
        }

    }

    public static void main(String[] args) {
        Supermercado sm = new Supermercado();
    }

    static synchronized void sumar(float n) {
        ingresos += n;
    }

    public static class Caja extends Thread {

        int ms;

        public Caja() {
            this.ms = (int) (Math.random() * 1500 + 1000);
        }

        @Override
        public void run() {
            System.out.println("Se están pasando los productos...");
            try {
                sleep(ms);
            } catch (InterruptedException ex) {
                ex.printStackTrace();
            }
        }
    }

    public static class Cliente extends Thread {

        int tiempo;
        float pago;

        public Cliente() {
            this.tiempo = (int) (Math.random() * 1000 + 500);
            pago = (float) (Math.random() * 50);
        }

        @Override
        public void run() {
            int nCaja = (int) (Math.random() * arrCajas.size());
            synchronized (arrCajas.get(nCaja)) {
                System.out.println("El cliente " + this.getName() + " va a comprar.");
                try {
                    sleep(tiempo);
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }

                try {
                    arrCajas.get(nCaja).wait();
                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
                System.out.println("El cliente " + this.getName() + " va a caja.");
                arrTCajas.get(nCaja).start();
                try {
                    arrTCajas.get(nCaja).join();

                } catch (InterruptedException ex) {
                    ex.printStackTrace();
                }
                System.out.println("El cliente " + this.getName() + " va a pagar " + pago);
                sumar(pago);
                System.out.println("La recaudación actual total es de " + ingresos);
                arrCajas.get(nCaja).notify();
            }

        }

    }
}