Producer Comsumer problem using wait() and notify(), in Java

ProducerConsumerProblem.java

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

/**
 * Created by fengchaoyi on 16/9/6.
 */

//Thinking in Java P703
public class ProducerConsumerProblem {
    public static void main(String[] args) {
        new Restaurant();
    }
}

class Restaurant {
    //    private ArrayList<Meal> mealArrayList;
    Meal newMeal;

    Waiter waiter;
    Chef chef;

    ExecutorService executorService = Executors.newCachedThreadPool();

    Restaurant() {
        this.newMeal = null;
        this.waiter = new Waiter(this);
        this.chef = new Chef(this);
        executorService.execute(waiter);
        executorService.execute(chef);
    }
}

class Waiter implements Runnable {
    private Restaurant restaurant;

    Waiter(Restaurant restaurant) {
        this.restaurant = restaurant;
        this.restaurant.waiter = this;
    }

    @Override
    public void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.newMeal == null) {
                        wait(); // wait for chef's notify()
                    }
                }
                Meal nextMeal = restaurant.newMeal;
                nextMeal.process();

                synchronized (restaurant.chef) {
                    // synchronized???
                    restaurant.newMeal = null;
                    restaurant.chef.notify();
                }
            }
        } catch (InterruptedException e) {

            System.out.println("Waiter interrupted");
        }
    }
}

class Chef implements Runnable {
    private Restaurant restaurant;
    private int count;

    private int materialCount = 10;

    Chef(Restaurant restaurant) {
        this.restaurant = restaurant;
        this.restaurant.chef = this;
        this.count = 0;
    }

    @Override
    public synchronized void run() {
        try {
            while (!Thread.interrupted()) {
                synchronized (this) {
                    while (restaurant.newMeal != null) {
                        wait(); // wait for waiter's notify()
                        // this lock of chef is automatically released, so that waiter.notify() can catch this lock
                    }
                }
                this.count += 1;

                if (this.count > this.materialCount) {
                    System.out.println("Running out of material. Closing...");
                    restaurant.executorService.shutdownNow();//not shutdown()
                }

                Meal newMeal = new Meal(this.count);
                TimeUnit.MILLISECONDS.sleep(100);
                restaurant.newMeal = newMeal;

                synchronized (restaurant.waiter) {
                    System.out.println("notify waiter for meal " + count + " ready.");
                    restaurant.waiter.notify();
                }
            }
        } catch (InterruptedException e) {
            System.out.println("Chef interrupted");
        }

    }
}

class Meal {
    private int number;

    Meal(int number) {
        this.number = number;
    }

    void process() {
        System.out.println("Meal " + this.number + " is being given to customer!");
    }
}