Is a java synchronized method entry point thread safe enough?

Question

I have a Singleton class handling a kind of cache with different objects in a Hashmap. (The format of a key is directly linked to the type of object stored in the map - hence the map is of )

Three different actions are possible on the map : add, get, remove.

I secured the access to the map by using a public entry point method (no intense access) :

public synchronized Object doAction(String actionType, String key, Object data){
  Object myObj = null;
  if (actionType.equalsIgnorecase("ADD"){
    addDataToMyMap(key,data);
  } else if (actionType.equalsIgnorecase("GET"){
    myObj = getDataFromMyMap(key);
  } else if (actionType.equalsIgnorecase("REM"){  
    removeDataFromMyMap(key);      
  }
  return myObj;
}

Notes:

The map is private. Methods addDataToMyMap(), getDataFromMyMap() and removeDataFromMyMap() are private. Only the entry point method is public and nothing else except the static getInstance() of the class itself.

Do you confirm it is thread safe for concurrent access to the map since there is no other way to use map but through that method ?

If it is safge for a Map, I guess this principle could be applied to any other kind of shared ressource.

Many thanks in advance for your answers.

David

Answer 1

I would need to see your implementation of your methods, but it could be enough. BUT i would recommend you to use a Map from the Collection API of java then you wouldnt need to synchronize your method unless your sharing some other instance.

read this: http://www.java-examples.com/get-synchronized-map-java-hashmap-example