Collections.synchronizedMap() vs. ConcurrentHashMap

java.util.Collections.synchronizedMap() method's declaration is as following:
public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m)

Collections.synchronizedMap() guarantees that each atomic operation I want to run on the map will be synchronized. It creates a blocking Map which will degrade performance, however it ensure consistency (if used properly).

Let's see at a sample code:
  Map<String, List<String>> myMap;
  myMap = new HashMap<String, List<String>>();
  private static Map<String, List<String>> synchroMap = Collections.synchronizedMap(myMap);

  public static void addToMyMap(String myKey, String myValue) {
    synchronized (synchroMap) {
      if (!synchroMap.containsKey(myKey)) {
        List<String> listOfValues = new ArrayList<String>();
        listOfValues.add(myValue);
        synchroMap.put(myKey, listOfValues);
      }else{
        synchroMap.get(myKey).add(myValue);
      }
    }
  }

And what about java.util.concurrent.ConcurrentHashMap?
It allows concurrent changes of the Map from several threads without the need to block them. We can use it when the performance is critical.