1) Singletons allow their factory methods to control the concrete class that is used, relieving the client of the burden. Static methods are bound at compile time, meaning that every client call has to make the decision of which static to call. E.g.,

class PrefManager{
    final PrefManager instance = isOsWindows
        ? new RegistryPrefManager()
        : new FilePrefManager();
    PrefManager getInstance(){
        return instance;
    }
    void savePref...
}

If statics were used here, the decision of where to save prefs would be left to the client everytime a pref is saved. Then if new pref managers were added, all the client calls that use it need to be updated.

2) Singletons can be passed around like normal objects. See Collections.EMPTY_LIST.

3) Singletons ensure that a constructor is called. Statics that share data must all check that it has been initialized before they work on it.

My answer is

If you class doesnot contain private constructor, it is possible to create more than one class right? so that singleton has come. If you are using static also giving problem when you are suing that same for difference object it will give conflit. that is why make it single class using singleton by using private constructor. without that private construtor how can we create a unique object and unique object handle.

Usually a singleton IS a static reference, in the class.