Singleton: synchronized, shared across Threads

LazySingletonThreadSafe3.java

public class LazySingleton {

    private LazySingleton() {
    }

    private static volatile LazySingleton sInstance;

    public static LazySingleton getInstance() {

        if  (sInstance == null) {
            synchronized (LazySingleton.class) {
                if (sInstance == null) {
                    sInstance = new LazySingleton();
                }
            }
        }
        
        return sInstance;
    }
}

Tutorial is here