Question

I’m learning Objective-C and I’m confused on what the difference is between an instance of a class and an object –- are they the same ?

Heres an example:

 NSString *name = [[NSString alloc]initWithString:@"Harry"]; 

*name is a pointer to the NSString class. @"Harry" is the value of the string. So is name an Object from the NSString class or is name called an instance of a class?

Another example from a Class I made:

  Rectangle *rect = [[Rectangle alloc]init];  

So *rect is a pointer. Is rect an Object or is it an instance of a class ?

Answer 1

In ObjectiveC, an instance of a class is always an object. And an object is always an instance of a class. An “object” is an instance of a class, a class which somewhere down the chain eventually inherits from NSObject. When you declare a class with no superclass, NSObject is the implicit superclass.

NSString *name = [[NSString alloc] initWithString:@"Harry"]; 

name is a pointer to an object, which more specifically is an instance of NSString that has a value of “Harry”. All NSString’s are objects.

Rectangle *rect = [[Rectangle alloc] init];

Same here. rect is a pointer to an object, which is an instance of Rectangle.