Friday, July 2, 2010

What is the difference bet ween object and instance

There is a lot of discussions on this topic over the internet. Some of the people says both are same and some of other says both are different. Here I am planning to share my overall view on this topic. As per my knowledge both are looks same but different. Here are the some useful points:
  • Instance is Logical but object is Physical means occupies some memory.
  • We can create an instance for abstract class as well as for interface, but we cannot create an object for those.
  • Object is instance of class and instance means representative of class i.e object.
  • Instance refers to Reference of an object.
  • Object is actually pointing to memory address of that instance.
  • You can’t pass instance over the layers but you can pass the object over the layers
  • You can’t store an instance but you can store an object
  • A single object can have more than one instance.
  • Instance will have the both class definition and the object definition where as in object it will have only the object definition.
Syntax of Object:
classname var=new classname();
But for instance creation it returns only a pointer refering to an object, syntax is :
classname varname;

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