OO Basics

[gunjan]

Hi all:
One of the my colleagues who is learning OO asked me a question, which I stumbled while answering.
Q:"What is the difference between object and instance".
answer: same
Q: why two diff names
answer: terminology.
Q: Any specific reason.
answer: will think about it.
Q: There must be some difference between the two?
what do you think.
Regards
Gunjan

[Tony Alicea]

I am moving this topic to the Object Oriented (OO) section where it will get the attention it deserves.

[Jim Yingst]

I think that the word "object" is kind of, ummm, overloaded. It can refer to the general concept of objects, as in "Object-Oriented Programming" (which is really just as much "Class-Oriented Programming"), or it can refer to the class Object (well really it doesn't unless you capitalize it, but this doesn't work in speech and people often get it wrong anyway), or, most commonly, it can refer to an instance. If you want to talk about an instance and be sure people know what you mean, it's safest to say "instance", IMO. I think people were using "object" first until they started using "instance" to resolve this ambiguity.

[Frank Carver]

In Java each object must be an instance of a class, so the terms are effectively synonymous, but this doesn't hold true for all OO languages.
Not all OO languages are class-based. One fairly common alternative is prototype-based OO (eg. Self, Brain etc.), where each object is a modification or specialization of another object. In such systems, no object is really an instance of anything, there are no classes, just objects.

[Tony Alicea]

Where would you put JavaScript? Under Object Oriented or Object Based? SOmething else? And what is the difference between OO and OB? Thanks.

[Frank Carver]

Object Based (OB) is usually used to mean a system which has objects (and probably classes) like an OO system, but only offers a limited ability to define and create your own objects. Both JavaScript and Visual Basic are commonly considered as part of this group :- defining a new class in JS is almost impossible. In VB it is at least possible, but not part of the main language syntax.

[Amit Zzz Kulkarni]

Frank,
You are close ,you should have said that OB don't have inheritance at all whereas OO was mostly inheritance until a few years ago ,now it's both Inheritance and Composition. An extreme form of composition is Delegation.
Rgds
Amit

Originally posted by Frank Carver:
Object Based (OB) is usually used to mean a system which has objects (and probably classes) like an OO system, but only offers a limited ability to define and create your own objects. Both JavaScript and Visual Basic are commonly considered as part of this group :- defining a new class in JS is almost impossible. In VB it is at least possible, but not part of the main language syntax.