Question

Coming from Java background I am guessing this is expected. I would really love to learn Objective-C and start developing Mac apps, but the syntax is just killing me.

For example:

-(void) setNumerator: (int) n
{
    numerator = n;
}

What is that dash for and why is followed by void in parenthesis? I’ve never seen void in parenthesis in C/C++, Java or C#. Why don’t we have a semicolon after (int) n? But we do have it here:

-(void) setNumerator: (int) n;

And what’s with this alloc, init, release process?

myFraction = [Fraction alloc]; 
myFraction = [myFraction init];
[myFraction release];

And why is it [myFraction release]; and not myFraction = [myFraction release]; ?

And lastly what’s with the @ signs and what’s this implementation equivalent in Java?

@implementation Fraction

@end

I am currently reading Programming in Objective C 2.0 and it’s just so frustrating learning this new syntax for someone in Java background.

UPDATE 1: After reading all these answers and Programming in Objective C 2.0 a little further, it’s all starting to make sense now!

UPDATE 2: Thanks for the great tip “support-multilanguage”. We can combine these two statements into one like so:

myFraction = [Fraction alloc]; 
myFraction = [myFraction init];

Can be reduced to:

myFraction = [[Fraction alloc] init]; 

Answer 1

What is that dash for and why is followed by void in parenthesis?

The dash - means “instance level” ( which is the default in Java ). When you see a plus sign + it means class level ( same as using static in Java )

The void in parenthesis is the return type see below.

Why don’t we have a semicolon after (int) n? But we do have it here:

-(void) setNumerator: (int) n;

Because that’s the method signature, you can think of it as a interface:

 interface YourClass {
      void setNumerator(int n );// see? semicolon
 }

Same situation.

Objective-C having roots in C ( actually this is the real C with objects ) needs a header file ( completely removed in Java ) where you define what the functions/methods your class would have.

The equivalent if such thing would exist in java would be:

// YourClass.java.h 

 interface YourClass {
      void setNumerator(int n );
 }
 // YourClass.java.m
 class YourClass {
      void setNumerator( int n ) {
       this.n = n;
      }
  }

And what’s with this alloc, init, release process?

myFraction = [Fraction alloc]; 
myFraction = [myFraction init];
[myFraction release];

allo-init is the equivalent for new in Java, alloc that’s when you ask for memory for your object, alloc request memory, and init calls the init method, equivalent to the Java class constructor ( btw Ruby does the same behind scenes )

There’s no equivalent to release in Java because it is garbage collected, in Objective-C you have to release your object.

BTW, the initialization could also be myFraction = [[Fraction alloc]init];

And lastly what’s with the @ signs and what’s this implementation equivalent in Java?

 @implementation Fraction

 @end

That’s the class definition as I mentioned earlier.

I am currently reading Programming in Objective C 2.0 and it’s just so frustrating learning this new syntax for someone in Java background.

Here’s a related answer that will help you to get more familiar with the square brackets:

Brief history of the “square brackets” is I remember it.