Question

in this site it says that a new object isnt being created each time , which leads to efficiency, but by what i can see an object is being created each time in the static method..

do not need to create a new object
upon each invocation – objects can be
cached and reused, if necessary.

http://www.javapractices.com/topic/TopicAction.do?Id=21

so why are the static factory methods are so efficient?

isnt writing something like this : Object obj=new Object is same as if i did Object obj=Someclass.GetObj();

class Someclass
{
   public static Object GetObj()
   {
     return new Object
   }
}

There is caching, but a new object is created either way…

Answer 1

They are more flexible – for example if the input parameters for new object are not valid, you can return null or some null object implementation (=instance, which does nothing, but will not break your code by NullPointerException), or, as previously mentioned by others, you can cache created instances. There is another benefit from using factory methods over constructors – you can name them whatever you like, which can be more readable, if there are multiple constructors with lots of optional parameters.

EDIT: if you want to use only one instance, you can use this simple factory:

class Someclass{
  private static Object o=new Object();

  public static Object getObj(){
    return o;
  }
}