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iOS Objective-C Basics (Retired) Foundation Framework NSNumber

Posted by Vlatko .
Vlatko .
2,526 Points

Can you help me understand the breakdown of this code?

Mainly, what I want to know is why the second line is written the way it's written and what the terms alloc and init mean. 

NSNumber *mike;
mike = [[NSNumber alloc] initWithInt:23];
NSLog(@"mike's number is %@", mike);

1 Answer

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

all objects in objective c are pointers, thats why you had to use the asterix before the obejcts name when you declared it here:

NSNumber *mike;

one of the advantages of using pointers with objects is that when you reference an object you arent referencing the object itself, but the memory address of the object. The memory address is tiny compared to the actual object, which makes it easy to pass around in your code.

NSNumbers are objects. objects must be allocated and initialized before they can be used. you can think of allocating and initializing objects as "creating them". allocation sets aside the memory for your object and init sets up your object. in this case you use

mike = [[NSNumber alloc] initWithInt:23];

which allocates memory for an NSNumber object, initializes it with the value 23, and returns the object. this object is assigned to the pointer mike. you can have multiple initializer methods for an object, NSNumber has many such as initWithFloat, initWithInt etc etc.you can even create custom initializer methods to customize the way your objects are set up when they are first created.

Michael Bowen
Michael Bowen
770 Points

All objects are not actually pointers, but you create a pointer that points to the object that is allocated in heap. Anything that you use alloc to create is placed in the heap, so you need a pointer to reference it.