Question

As i was reading through the book on Objective-C, i came across an example that initialized a class as follows:

ClassName *p = [[ClassName alloc] init]; 

While it makes sense that first we need to allocate memory to store data ClassName has before initializing, the following works just as well:

ClassName *p = [ClassName alloc]; 

Is init always needed?

Answer 1

In theory, it’s not technically required. That’s because NSObject‘s init method is effectively just return self;. However, in practice, it’s absolutely essential. Objects perform internal setup inside the init method – creating internal state, allocating private members, and generally getting ready for action. The init method may not even return the same object as you allocated.

Think of it in two phases: alloc allocates memory, but that’s it – it’s analogous to Java’s new. init configures the state of the memory so that the object can perform it’s tasks – analogous to Java calling the constructor. Don’t leave it out!