TweetFollow Us on Twitter

Apr 97 Getting Started

Volume Number: 13 (1997)
Issue Number: 4
Column Tag: Getting Started

A First Look at Objective-C

By Dave Mark, ©1997, All Rights Reserved. http://www.spiderworks.com

Well, it finally happened. Apple made their OS decision, catching many of us by surprise. Personally, I am very excited by Apple's move. As was clear from the energy at Macworld Expo, things are finally moving. Apple has made a bold move. Now we have to retool and rethink our programming strategies.

As Apple made clear, the System 7.5 version of the Mac Toolbox still has some significant legs and will likely be part of our lives for some time to come. As I write this, the announced release schedule for Rhapsody (code name for the new OS) does not show a significant beta in our hands until January of next year. Nothing to complain about there. Of course, it will take time for Apple to marry their technology to that of NeXT and we all want this job done right.

My point is that there are some important decisions we all have to make, but the current schedule gives us the luxury of continuing down the current path (System 7.5 apps) without penalty, while giving us the time to plan for the new order.

What About Be?

Before we move on to the main focus of this column, I'd like to take a second to talk about the apparent loser in the OS wars: Be, Inc. You might think that because Be was not able to work out a deal with Apple, they have become damaged goods. Not so! As anyone who attended the first ever Be developer's conference will tell you, the BeOS is cool, the commitment from developers is there, and there's an excitement in the air, a feeling of being in on the ground floor of something big.

Bottom line, we now have two technological evolutions to follow. Things are about to get very interesting.

Java, C, C++, and Pascal vs. Objective-C

There are a number of questions raised by Apple's acquisition of NeXT. (See this month's Factory Floor interview with Avie Tevanian, Apple's new OS boss.) Among them, in what programming language will Rhapsody development be done? Is Objective-C the new sheriff in town? Will we be able to continue our C/C++ and Pascal efforts? And what about Java?

As we go to press, these issues are still not finalized. The story so far seems to be "all of the above." Objective-C is the language for NEXTSTEP, and should provide the most intimate access to Rhapsody. So far, it looks like C, C++, Pascal, etc. will all be supported, though in a slightly more distant relationship. Objective-C and Java support dynamic binding. C and Pascal support static binding, and C++ supports late binding.

In a nutshell, binding connects a called function to the function caller. Static binding means that the function being called is determined as the program is compiled. Though you can use function pointers to delay binding decisions in C, typically your binding decisions are made when you compile.

Dynamic binding is the opposite of static binding. The binding decision is delayed until runtime. This allows you to add components to your program while it is still running. If the runtime environment is designed to support this (and Rhapsody should be), it opens up a lot of interesting possibilities.

The C++ language supports a limited version of dynamic binding called late binding. In C++, a function call must type-match exactly the called function (called static typing) or else type-match exactly an inherited function. Though C++ virtual functions allow you to delay the binding until runtime, the type constraints still apply. Late binding is still restricted. Dynamic binding is unconstrained.

Java uses the same binding mechanism as Objective-C. Java offers the advantage of being a cross-platform solution, as well as tightly integrated with the Internet. It seems likely that Java will continue to grow and is likely to play a large role in Rhapsody.

What does all this mean for you? If you've been following this column over the past few months, you've already gotten a handle on Java. Over the next few months, we'll dig into Objective-C, starting with a review of some object programming terminology and a first look at the language syntax.

Finally, you can call the NeXT order desk at 800-TRY-NEXT (800-879-6398) to order books, manuals and software directly from NeXT, including "OpenStep Object-Oriented Programming and the Objective-C Language", "Enterprise Objects Framework Developer's Guide (for EOF 2.0)", "Working with Interface Builder (for Enterprise Objects Framework)", and "Discovering OPENSTEP: A Developer Tutorial (for Windows NT)."

Some Object Programming Terminology

Before we move on to the basics of Objective-C syntax, let's review a bit of object programming terminology, just to make sure we are all on the same page. We've already talked about dynamic, static, and late binding. Here are a few more.

Instances, methods, and instance variables. Just as in C++, an Objective-C class definition is a template for the creation of individual objects, also known as instances. The functions within a class (member functions) are known as methods, and the variables (data members) are known as instance variables.

Messages

In C++, an object's member function gets called. In Objective-C, a message is sent to an instance, known as the receiver. At runtime, the appropriate receiver method capable of handling the message is determined and the method is called.

Interface, implementation, and encapsulation

The interface to a class is the set of external methods defined for that class. The implementation is the internal workings of the class. The idea here is to keep the inner workings hidden from the user of a class, forcing them to access an instance via its interface. This mechanism is known as encapsulation. In Objective-C, all instance variables are encapsulated and access to them is limited to methods defined for the class.

Inheritance

Inheritance in Objective-C works pretty much as it does in C++. The parent class is known as a superclass and derived classes are known as subclasses.

A First Look at the Objective-C Language

Objective-C starts off with all the standard syntax of C. Objective-C source code files use the extension ".m", while header files stick with the extension ".h".

Objective-C features a generic object pointer type called id.

id myObject;

An id is designed as a generic pointer to an object's instance variables. The previous line of code didn't actually allocate an object. It created a pointer which will eventually be used to allocate the object. nil is defined as an id with a value of 0.

By using a generic object pointer type, Objective-C delays the type binding decisions until run time. This is a good thing, but it also puts a bit of extra overhead on the run-time system. Basically, in the NeXT world, all objects are derived from the root class Object. Object features an isa variable which is inherited by all Object subclasses (which should be all classes in your program). The isa instance variable specifies the class to which the object belongs.

Earlier, we talked about the separation of interface and implementation. In Objective-C, you declare the classes interface like this

 MySuperClass
{
 instance variable declarations
}
method declarations

Objective-C supports the standard C compiler directives that start with "#". In addition, Objective-C adds Objective-C specific compiler directives which start with "@". As you might expect, class names start with an upper case letter and variable names with a lower case letter. By convention, all identifiers are named using intercaps, yielding names like myVariable and MyClass.

Instance variable declarations are done just as they are in C and C++, though the type "id" is used pretty frequently in Objective-C and, obviously, is not built in to C or C++.

Method declarations are pretty funky. Here's a sample:

- (int)getX:(int)x andY:(int)y;

The leading minus sign marks this function as an instance method. A leading plus sign ("+") marks the method as a class method. (A class method is sort of like a static method in C++. We'll talk about class objects and class methods in a future column.)

The return type is specified in parentheses, just as if it were a typecast. If you leave off the return type, it defaults to the type id (just as a C function defaults to int if you leave off the return type). Note that a function that is not a method still defaults to a return type of int.

The name of the method specified above is getX:andY: and includes the colons in the name. Weird, eh? The idea is to have each chunk of the method end with a colon and correspond to a parameter. In this case, there are two parameters, x and y. The type of each parameter is also specified by a typecasting-like mechanism. Both x and y are ints.

Here's another example:

- getObj1:object1 andObj2:object2;

Note that this time all the type information was left out of the declaration. The return type and type of both arguments are the same, the default type "id".

Here's a sample class interface:

#import "Object.h"

 Object
{
 idmyVar;
}
- init;
- getLastObject:lastObject;

This interface declares a class named MyClass derived from the class Object. MyClass features a single variable, an id named myVar, and two methods, one named init and one named getLastObject, both of which return an id.

Note that the interface, which lives in a ".h" file, starts off with a #import compiler directive. #import replaces the #ifdef business you use in C++ to make sure you don't include an include file twice. Use #import to include any header files you need to include. Alternatively, you can just declare the classes you reference using the @class directive.


This directive tells the compiler that Object is a class. That's it. This delays any type analysis until run-time and can solve some knotty cross-dependancy problems where classes refer to each other. Bottom line, use the @class directive if you can get away with it, otherwise #import the classes' header file.

The implementation of a class looks like this:

 MySuperClass
{
 instance variable declarations
}
method definitions

Gee, doesn't this look familiar? Yup, the implementation looks almost identical to the interface. The differences? The implementation lives in a ".m" file instead of in a ".h" file and the method definitions replace the method declarations in the interface. Also, you are required to #import your classes' interface file in the implementation file. One nice benefit of this last fact is that you can leave the superclass and the instance variable declarations out of the implementation.

Here's another look:

#import "MyClass.h"

Till Next Month...

Hopefully, you've got a feel for the basic structure of an Objective-C program. Next month, we'll talk about message receivers and message syntax, and present our first Objective-C program. To get a head start, check out the Objective-C specification on the NeXT web site. (See the URL earlier in the column.) You can buy the NEXTSTEP environment running under NeXT, WinNT, and on top of Mach. Also, you might want to check out CodeBuilder from Tenon InterSystems. CodeBuilder runs on a Mac and comes with (among a LOT of other stuff) an Objective-C compiler. You might also want to check out Apple's web site to find out the current release schedule for Rhapsody tool betas and the Metrowerks web site to find the status of their Rhapsody tools.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

1Password 5.1 - Powerful password manage...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
GarageSale 6.9.2 - Create outstanding eB...
GarageSale is a slick, full-featured client application for the eBay online auction system. Create and manage your auctions with ease. With GarageSale, you can create, edit, track, and manage... Read more
calibre 2.17 - Complete e-library manage...
Calibre is a complete e-book library manager. Organize your collection, convert your books to multiple formats, and sync with all of your devices. Let Calibre be your multi-tasking digital librarian... Read more
OmniGraffle Pro 6.1.2 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
OmniGraffle 6.1.2 - Create diagrams, flo...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
RoboForm 2.0.2 - Password manager; syncs...
RoboForm is a password manager that offers one-click login, mobile syncing, easy form filling, and reliable security. Password Manager. RoboForm remembers your passwords so you don't have to! Just... Read more
Apple MainStage 3.1 - Live performance t...
Love the sound you got on your recording? MainStage 3 makes it easy to bring all the same instruments and effects to the stage. Everything from the Sound Library and Smart Controls you're familiar... Read more
Freeway Pro 7.0.2 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
A Better Finder Rename 9.44 - File, phot...
A Better Finder Rename is the most complete renaming solution available on the market today. That's why, since 1996, tens of thousands of hobbyists, professionals and businesses depend on A Better... Read more
Stacks 2.6.9 - New way to create pages i...
Stacks is a new way to create pages in RapidWeaver. It's a plugin designed to combine drag-and-drop simplicity with the power of fluid layout. Features: Fluid Layout: Stacks lets you build pages... Read more

This Week at 148Apps: January 19-23, 201...
Warm Your Winter With New Apps!   How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you’re looking for. The ones we love become Editor’s Choice, standing out... | Read more »
Eggmaster Review
Eggmaster Review By Jennifer Allen on January 26th, 2015 Our Rating: :: BRIEFLY COMPELLINGUniversal App - Designed for iPhone and iPad Tap like crazy to gain eggs, so that you can buy upgrades to gain more eggs, and so on. It... | Read more »
Cloudy Or Dry – Funny Or Die Release a W...
Cloudy Or Dry – Funny Or Die Release a Weather App Posted by Ellis Spice on January 26th, 2015 [ permalink ] iPhone App - Designed for the iPhone, compatible with the iPad | Read more »
Mediocre, the Team Behind Smash Hit, is...
Mediocre, the Team Behind Smash Hit, is Teasing Their Latest Unnamed Project Posted by Jessica Fisher on January 26th, 2015 [ permalink ] | Read more »
Heroes of Gaia Review
Heroes of Gaia Review By Campbell Bird on January 26th, 2015 Our Rating: :: TIMERS OF MIGHT AND MAGICUniversal App - Designed for iPhone and iPad This free-to-play rpg looks a lot like Heroes of Might and Magic, but it’s poor... | Read more »
Choice Provisions is Set to Launch Destr...
Choice Provisions is Set to Launch Destructamundo on iOS This Month Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] Choice Provisions – home stable to | Read more »
King of Thieves – An Interview With Zept...
Ahead of the release of ZeptoLab’s King of Thieves, we were able to ask ZeptoLab’s co-founder, Semyon Voinov, a few questions about the inspiration behind the game and what that means for the Cut the Rope franchise. | Read more »
Handle Review
Handle Review By Jennifer Allen on January 23rd, 2015 Our Rating: :: SPEEDY ORGANIZINGUniversal App - Designed for iPhone and iPad Handle is a very convenient way of juggling your emails, To Do list, and Calendar all through one... | Read more »
The New Disney Inquizitive App Offers a...
The New Disney Inquizitive App Offers a Place for Fans to Take Disney Quizzes Posted by Tre Lawrence on January 23rd, 2015 [ permalink ] | Read more »
Hands-On With Cut the Rope Developer Zep...
Marking quite a departure from ZeptoLab’s past successes, namely the Cut The Rope series, King of Thieves is shaping up to be quite promising. Due for release in February, we were lucky enough to have some time with a preview build to see exactly... | Read more »

Price Scanner via MacPrices.net

Petitioning Dropbox For Mac OS X 10.4 and 10....
Last week Dropbox announced to its users that app support for Mac OS X 10.4 and 10.5 will end May 18 — disappointing news for those of us who are still getting useful service out of older PPC Macs... Read more
Stop Street Harassment, Bullying, and Assault...
The STOP-ATTACK (http://www.stop-attack.com) app will leverage smartphone technology to make the world a safer place. Whether it’s bullying, street harassment or something even more sinister, the app... Read more
Stir Kinetic Desk M1 Standing Or Sitting Desk...
The age of the standing desk is upon us, and according to medical research, it’s arriving none too soon. The World Health Organization (WHO), reports that 60 to 85 percent of people worldwide lead... Read more
Bosch Opens North American eBike Conversion H...
Following its entry into the U.S. eBike market in early 2014, Bosch has established a new headquarters office for Bosch eBike Systems (http://www.bosch-ebike.us) in Southern California, expanding the... Read more
13-inch 2.4GHz Retina MacBook Pro (Apple refu...
The Apple Store has previous-generation Apple Certified Refurbished 13″ 2.4GHz/128GB Retina MacBook Pros available for $999. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.4GHz/... Read more
13-inch 2.6GHz Retina MacBook Pro on sale for...
Adorama has the 13″ 2.6GHz/128GB Retina MacBook Pro on sale for $1189.99, $110 off MSRP. Shipping is free, and Adorama charges NY & NJ sales tax only. Read more
College Student Deals are back, additional $5...
Take an additional $50 off all MacBooks and iMacs at Best Buy Online with their College Students Deals Savings, valid through April 11, 2015. Anyone with a valid .EDU email address can take advantage... Read more
iPhone 6 and 6 Plus GIve Apple Half Of US Mob...
Chicago-based Consumer Intelligence Research Partners, LLC (CIRP) have released analysis of the results of its research on mobile phone manufacturers for the calendar quarter that ended December 31,... Read more
Save $100 on MacBook Airs with 256GB of stora...
B&H Photo has 256GB MacBook Airs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.4GHz/256GB MacBook Air: $999 $100 off MSRP - 13″ 1.4GHz/256GB MacBook... Read more
21-inch 2.7GHz iMac on sale for $1179, save $...
B&H Photo has the 21″ 2.7GHz iMac on sale for $1179 including free shipping plus NY sales tax only. Their price is $120 off MSRP, and it’s the lowest price available for this model from any... Read more

Jobs Board

Detailer *Apple* Ford Body Shop / Collision...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
*Apple* Acura/Subaru Service Technicians - A...
Apple Automotive is one of the fastest growing dealer…and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive , Read more
Business Development Manager - *Apple* Pay...
**Job Summary** Apple Pay is seeking an experienced business development manager to support the identification, recruitment, negotiation and ongoing management of Read more
*Apple* Solutions Consultant (ASC)- Retail S...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.