Java Program to demonstrate ConcurrentHashMap

ConcurrentHashMapExample.java:
import java.util.Enumeration;
import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapExample {
   
   public static void main(String[] args) {
       ConcurrentHashMap vehicles = new ConcurrentHashMap();
       
       // Add some vehicles.
       vehicles.put("BMW", 5);
       vehicles.put("Mercedes", 3);
       vehicles.put("Audi", 4);
       vehicles.put("Ford", 10);
       
       System.out.println("Total vehicles: " + vehicles.size());
       
       // Iterate over all vehicles, using the keySet method.
       for(String key: vehicles.keySet())
           System.out.println(key + " - " + vehicles.get(key));
       System.out.println();
       
       String searchKey = "Audi";
       if(vehicles.containsKey(searchKey))
           System.out.println("Found total " + vehicles.get(searchKey) + " "
                   + searchKey + " cars!\n");
       
       Enumeration elems = vehicles.elements();
       while(elems.hasMoreElements())
           System.out.println(elems.nextElement());
       System.out.println();
       
       Integer val = vehicles.putIfAbsent("Audi", 9);
       if(val != null)
           System.out.println("Audi was found in the map and its value was updated!");
       
       val = vehicles.putIfAbsent("Nissan", 9);
       if(val == null)
           System.out.println("Nissan wasn't found in map, thus a new pair was created!");
       System.out.println();
       
       // The next statements throw a NullPointerException, if uncommented.
       //vehicles.put("Nissan", null);
       //vehicles.put(null, 6);
       
       // Clear all values.
       vehicles.clear();
       
       // Equals to zero.
       System.out.println("After clear operation, size: " + vehicles.size());
   }
}
A sample execution is shown below:
Total vehicles: 4
BMW - 5
Mercedes - 3
Audi - 4
Ford - 10
Found total 4 Audi cars!
5
3
4
10
Audi was found in the map and its value was updated!
Nissan wasn't found in map, thus a new pair was created!
After clear operation, size: 0