Question

init method is declared in NSObject class hence, the client code can create a new instance of my singleton class, is there any way to achieve the real singleton such that client cannot create a new instance.

Answer 1

init method is for initialization of instance variables. on its own will not create the object. Alloc, copy methods needs to be overridden to achieve a real single ton.

Hope this should clarify.

+ (id)alloc {
    NSLog(@"%@: use +sharedInstance instead of +alloc", [[self class] name]);
  return nil; 
}
+ (id)new {
 return [self alloc];
}

+ (SingletonClass *)sharedInstance {
static SingletonClass *myInstance = nil; 
 if (!myInstance)
 {
    myInstance = [[super alloc] init];
 }
 return myInstance; 
}