Objective-C iOS Development for Legacy & Enterprise Apps · Lesson

Classes, Objects, and Methods

Learn to define classes, create objects, and implement instance and class methods to encapsulate behavior.

Classes, Objects, and Methods is a free Objective-C iOS Development for Legacy & Enterprise Apps lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Objective-C iOS Development for Legacy & Enterprise Apps learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

OOP Basics: Classes & Objects

Welcome to Object-Oriented Programming (OOP) in Objective-C! OOP helps organize code into reusable blueprints called classes.

From these blueprints, we create individual items called objects. Think of a class as a cookie cutter, and an object as a cookie!

Your First Class: Header File

Every Objective-C class has two main files: a .h (header) and a .m (implementation) file.

The header file (.h) declares what your class is and what it can do. It's like the public blueprint.

Here's how to declare a simple Person class:

// Person.h
#import <Foundation/Foundation.h>

@interface Person : NSObject

// Method declaration
- (void)sayHello;

@end

Class Implementation: Source File

The implementation file (.m) contains the actual code that makes your class work. It defines the behavior declared in the header.

Here, we implement the sayHello method for our Person class:

// Person.m
#import "Person.h"

@implementation Person

- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}

@end

Bringing Classes to Life: Objects

Now that we have a Person class, let's create an object from it! Creating an object is also called instantiation.

In Objective-C, we use the alloc and init methods to create new objects. alloc reserves memory, and init initializes it.

Try running this example:

#import <Foundation/Foundation.h>

// Person.h (declared here for runnable example)
@interface Person : NSObject
- (void)sayHello;
@end

// Person.m (implemented here for runnable example)
@implementation Person
- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    // Create a Person object
    Person *person1 = [[Person alloc] init];
    NSLog(@"Created a Person object: %@", person1);
  }
  return 0;
}

Instance Methods: Object Actions

Instance methods are actions that an individual object can perform. They usually work with data specific to that object.

To tell an object to perform an action, you send it a message. The syntax is [object methodName];.

Let's make our person1 object say hello:

#import <Foundation/Foundation.h>

@interface Person : NSObject
- (void)sayHello;
@end

@implementation Person
- (void)sayHello {
  NSLog(@"Hello from a Person object!");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    Person *person1 = [[Person alloc] init];
    [person1 sayHello]; // Sending the 'sayHello' message
  }
  return 0;
}

Methods with Arguments

Methods can also take arguments (or parameters) to customize their behavior. Objective-C uses a unique syntax for method arguments, making methods very descriptive.

The first argument is part of the method name, and subsequent arguments are labeled.

Let's add a method to our Person class that takes a name:

#import <Foundation/Foundation.h>

@interface Person : NSObject
- (void)sayHelloTo:(NSString *)name; // Method with one argument
@end

@implementation Person
- (void)sayHelloTo:(NSString *)name {
  NSLog(@"Hello, %@ from a Person object!", name);
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    Person *person1 = [[Person alloc] init];
    [person1 sayHelloTo:@"Alice"]; // Sending message with argument
  }
  return 0;
}

Class Methods: Type Actions

Unlike instance methods, class methods (also known as static methods) belong to the class itself, not to a specific object.

They start with a + sign in their declaration and implementation. You call them directly on the class name, like [ClassName methodName];.

Class methods are often used for creating objects or utility functions related to the class.

#import <Foundation/Foundation.h>

@interface Person : NSObject
+ (void)aboutThisClass; // Class method declaration
@end

@implementation Person
+ (void)aboutThisClass {
  NSLog(@"This is the Person class, used to create person objects.");
}
@end

int main(int argc, const char * argv[]) {
  @autoreleasepool {
    [Person aboutThisClass]; // Calling a class method
  }
  return 0;
}

Class vs. Instance: Key Difference

Here's a quick summary of the main differences:

Instance Methods (-): Operate on a specific object's data. You need an object instance to call them.
Class Methods (+): Operate on the class itself, not an instance. You call them directly on the class name. They don't have access to instance variables.

Choose the right type based on whether the action needs specific object data or general class-related functionality.

Sending Messages in Objective-C

In Objective-C, calling a method is formally called sending a message to an object (or class).

The syntax [receiver messageName:argument]; means we're sending the messageName: message to the receiver object (or class).

This message-sending mechanism is a core part of Objective-C's dynamic nature.

Quick Check: Classes & Methods

Test your knowledge of Objective-C OOP fundamentals.

Recap: Classes, Objects & Methods

Great job! In this lesson, you learned:

What classes are (blueprints) and objects are (instances).
How to declare a class in a .h file and implement it in a .m file.
How to create objects using alloc and init.
The difference between instance methods (-) and class methods (+).
How Objective-C uses message sending to invoke methods.

You're now ready to build more complex, organized Objective-C applications!

Frequently asked questions

Is the “Classes, Objects, and Methods” lesson free?

Yes — the full text of “Classes, Objects, and Methods” is free to read here on the web, and the Objective-C iOS Development for Legacy & Enterprise Apps course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Objective-C iOS Development for Legacy & Enterprise Apps course, upgrade to CoddyKit PRO.

What will I learn in “Classes, Objects, and Methods”?

Learn to define classes, create objects, and implement instance and class methods to encapsulate behavior. You practise Objective-C iOS Development for Legacy & Enterprise Apps with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Objective-C iOS Development for Legacy & Enterprise Apps?

No prior experience is required. Objective-C iOS Development for Legacy & Enterprise Apps on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Classes, Objects, and Methods” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Objective-C iOS Development for Legacy & Enterprise Apps lesson?

Yes. Every Objective-C iOS Development for Legacy & Enterprise Apps lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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