Java Thread synchronized on LinkedHashMap

import java.util.ArrayList;
import java.util.HashSet;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Random;
import java.util.Set;

public class Main {
   Map<String, Integer> inventoryMap = new LinkedHashMap<String, Integer>();
   List<CustomerOrder> customerOrders = new ArrayList<CustomerOrder>();
   Random random = new Random();
   Set<Thread> orderingThreads = new HashSet<Thread>();

   public static void main(String[] args) throws InterruptedException {
      new Main().start();
   }//from  www.  j  a  va2  s.  c om
   private void start() throws InterruptedException {
      for (int i = 0; i < 100; i++) {
         inventoryMap.put("Book #" + i, 1000);
      }
      for (int i = 0; i < 20; i++) {
         createOrderingThread();
      }
      Thread.sleep(100);
      checkInventoryLevels();
      Thread.sleep(100);
      for (Thread thread : orderingThreads) {
         thread.interrupt();
      }
      Thread.sleep(1000);
      checkInventoryLevels();
      displayOrders();
   }

   private void displayOrders() {
      synchronized (inventoryMap) {
         for (CustomerOrder order : customerOrders) {
            System.out.println(order.getQuantityOrdered() + " " + order.getItemOrdered() + " for " + order.getCustomerName());
         }
      }
   }

   private void createOrderingThread() {
      Thread orderingThread = new Thread(new Runnable() {
         public void run() {
            while (!Thread.interrupted()) {
               createRandomOrder();
            }
         }
      });
      orderingThread.start();
      orderingThreads.add(orderingThread);
   }

   private void createRandomOrder() {
      String itemOrdered = "Book #" + random.nextInt(100);
      int quantityOrdered = random.nextInt(2) + 1;
      String customerName = "Customer :" + System.currentTimeMillis();
      fulfillOrder(itemOrdered, quantityOrdered, customerName);
   }

   private boolean fulfillOrder(String itemOrdered, int quantityOrdered, String customerName) {
      synchronized (inventoryMap) {
         int currentInventory = inventoryMap.get(itemOrdered);
         if (currentInventory < quantityOrdered) {
            System.out.println("Couldn't fulfill order for " + customerName + " not enough " + itemOrdered + " ("
                  + quantityOrdered + ")");
            return false; // sold out
         }
         inventoryMap.put(itemOrdered, currentInventory - quantityOrdered);
         CustomerOrder order = new CustomerOrder(itemOrdered, quantityOrdered, customerName);
         customerOrders.add(order);
         System.out.println("Order done for " + customerName + " of " + itemOrdered + " (" + quantityOrdered + ")");
         return true;
      }
   }

   private void checkInventoryLevels() {
      synchronized (inventoryMap) {
         for (Map.Entry<String, Integer> inventoryEntry : inventoryMap.entrySet()) {
            System.out.println("Inventory Level :" + inventoryEntry.getKey() + " " + inventoryEntry.getValue());
         }
      }
   }
}

class CustomerOrder {
   String itemOrdered;
   int quantityOrdered;
   String customerName;

   CustomerOrder(String itemOrdered, int quantityOrdered, String customerName) {
      this.itemOrdered = itemOrdered;
      this.quantityOrdered = quantityOrdered;
      this.customerName = customerName;
   }

   public String getItemOrdered() {
      return itemOrdered;
   }

   public int getQuantityOrdered() {
      return quantityOrdered;
   }

   public String getCustomerName() {
      return customerName;
   }
}