singleton pattern in java. lazy initialization

Question

public static MySingleton getInstance() {
 if (_instance==null) {
   synchronized (MySingleton.class) {
      _instance = new MySingleton();
   }
 }
 return _instanc         


        

Answer 1

The second one is thread safe, but it has the overhead of synchronized on every call, no matter if the instance is constructed or not. The first option has one major flaw that it doesn't have a check for if (_instance == null) in the synchronized block to prevent creating two instances.