Why to use [super init] in Objective C constructors?

Question

Say I have a class named Item. Which is a superclass of NewsItem and TwitterItem.

If I want to create some NewsItem's do I have to use (inside constructor)

    self = [super init];

If yes, why? In Java/C# I would just do,

    NewsItem n = new NewsItem();

I don't have to do anything with superclasses in Java/C#. Just can't grasp it.

possible duplicate of [Why should I call self=\[super init\]](http://stackoverflow.com/questions/2956943/why-should-i-call-self-super-init) — jscs, Feb 14 '12 at 19:43

score 6 · Accepted Answer · answered Feb 14 '12 at 19:38

In Java and C#, the compiler automatically makes your constructor call the superclass constructor if you don't explicitly call it. For example, the “Java Tutorials” say this:

If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass. If the super class does not have a no-argument constructor, you will get a compile-time error. Object does have such a constructor, so if Object is the only superclass, there is no problem.

In Objective-C, the compiler doesn't do it automatically, so you have to do it yourself.

This was exactly the explanation I wanted. Thanks – xrDDDD Feb 15 '12 at 23:40 — xrDDDD, Feb 15 '12 at 23:40

score 5 · Answer 2 · edited Feb 14 '12 at 19:34

5

Because your superclass (and your superclass's superclass) need a chance to initialize, too.

And, keep in mind, that your superclass will [rarely] return nil or a different instance.

Which is why you do:

- (id)init
{
    self = [super init];
    if (self) {
        ... init stuff ....
    }
    return self;
}

edited Feb 14 '12 at 19:34

Lily Ballard

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answered Feb 14 '12 at 19:32

bbum

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Kevin added the return type. Thanks. Not strictly necessary as (id) is the default, but I prefer it, too. – bbum Feb 14 '12 at 22:57

score 1 · Answer 3 · edited Feb 14 '12 at 19:39

1

Because you are overriding the init message. If you don't override it then [[NewsItem alloc] init] would just call the superclass' init message. In C#, you might use base to do the same.

edited Feb 14 '12 at 19:39

NJones

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answered Feb 14 '12 at 19:34

typeoneerror

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score 0 · Answer 4 · answered Feb 14 '12 at 19:32

0

since your custom object will at least inherit from the mothers of all Objects: NSObject, you have to call '[super init];' 'super' simply does call the init Method of its superclass

answered Feb 14 '12 at 19:32

pmk

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Why to use [super init] in Objective C constructors?

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