The document discusses various topics in Objective-C including variables, data types, categories, protocols, and composite objects. It provides code examples to illustrate initializing objects, variable scope, enumerated data types, typedefs, data type conversion, categories, class extensions, protocols, delegates, and composite objects in Objective-C and compares some of these concepts to Java.

1. More On Variable,
Categories and Protocols
Chhorn Chhaly
Leang Bunrong
Cheng Udam
Kan Vichhai
Srou Chanthorn
Em Vy
Seth Sambo
Chea Socheat

2. Content
1. More on Variables and Data Types
 Initialize Objects
 Scoped Revisited
 More on properties, Synthesized Accessors, and Instance Variables
 Global Variable
 Static Variable
 Enumerated Data Types
 The typedef statement
 Data Type Convers

3. • Categories and Protocols
 Categories
 Class Extensions
 Protocols and Delegation
 Composite Object

4. Initializing Objects
• We initializing object by calling “init” method
• For example Fraction *f=[[Fraction alloc]init];
• The example above we just get an Object that has nothing or field value
• If we want to initialize object with many fields value, we have to create our custom
method to initialize object

5. Objective-C Java

6. Initializing Objects
• The method initWithNumerator:(int)n withDenominator:(int)d is the custom method to
initializing object
• All initializing methods must start with word “init…..”
• Self=[super init] means the super class calls “init” method to initialize for current object
• But it just an object without any fields value
• After that line we see that we initialize _numerator and _denomitor
• Then we return “self” that fulfill of object with field values

7. Variable Scope
In Objective-C, a variable has been declared it may or may not be accessible to other
sections of the program code. This accessibility depends on where and how the variable
was declared and where the code is that needs to access it. This is know as variable
scope.

8. Local Variables
Variables that are declared inside a function or block are called local variables. They can
be used only by statement that are inside that function or block of code. Local variable
are not known to functions outside their own.
Example:
Objective-C:
-(void) sum:(int) x secondP:(int) y {
int total;
total = x+y;
NSLog(@”Total: %i”, total);
}
NSLog(@”Total: %i”, total);
// illegal Total is now out of scope.
Java:
public void sum(int x, int y){
int total;
total = x+y;
System.out.println(“Total: ” + total);
}
System.out.println(“Total: ”+ total);
// illegal Total is now out of scope.

9. Global Variables
Global variables are defined outside of a function, usually on top of the program. A global variable can be accessed by any
function. That is, a global variable is
Objective-C
#import <Foundation/Foundation.h>
Int myVar = 321;
Int main (int argc, conts char * argv[]){
@autoreleasepool{
NSLog(@”myVar = %i”, myVar);
}
return 0;
}
The second file, named display.m contain the code for
the displayit() function.
#import <Foundation/Foundation.h>
extern int myVar;
void displayit(){
NSLog(@”MyVar from different source file is i%”, myVar);
}
Java
Public class Global{
Int myVar = 321;
public static void main (String args[]){
System.out.println(“myVar = ”+ myVar);
}
void displayit(){
System.out.println(“myVar = ”+myVar);
}
}

10. Multiple Classes In .h file
 In the Models.h file we declare two classes

11. Multiple Classes in .h file(cont.)
 Import Models.h we get two classes

12. Accessing static and non static field to category
 Models class(.h.m)

13. Accessing static and non static field to category
 Calling static field(check) and non static field(modelsfield) to MyCatagory.

14. Enumerated Data Types
• Enumerated Type : Is an user-defined type that is used in Objective-C to represent the
data that can be stored in one of several predefined values (all of them are int).
• What is it’s purpose : The purpose of enumerated types is to create specifically named
constants.
• Syntax : enum name_of_enumerator { element1, element2,…};
• enum : tell compiler to create enumeration
• name_of_enum : is the name to be assigned the enumeration
• element: field are the name that can be used to set variable

15. Enumerated Data Types
NOTE :
• enumerators use numbers corresponding to the element
• By default the first value corresponds to 0, the second to 1 and so on
• It is also possible to specify the values used by each value name
enum temperatureTypes{
cold = 10, // (redefined up = 10)
warm, // down will 11 (increment one from previous)
hot = 95, // (redefined left = 95)
veryhot // right will 96 (increment one from previous)
};
Example

16. The Typedef Statement
• The Typedef Statement : allows the programmer to define one Objective-C type as
another.
• To define a new typedef :
• Write the statement as if a variable of the original type was being declared
• Where you would put the name of the variable (after the type), place the new type name.
• Prefix everything with typedef

17. The Typedef Statement
• Syntax:
• Example:
in this example above, define the name Counter to be equivalent to the Objective-C
data type int.
The second line we declare variable to be type of Counter.
typedef DataType variable;
typedef int Counter;
Counter i, j;

18. Data Type Conversion
• Type casting is a way to convert a variable from one data type to another data type.
• In Objective-C when we evaluation of the two operands, type of the result is convert to
the big size between the two operands automatically but except char, short int or of an
enumarated data type they are converted to int.
• Example: Output

19. • Example:
Output

20. Data Type Conversion (cont.)
• In Objective-C is almost the same with Java but still have a little bit different below:
• In Java long and short are data type but in Objective-C is not so it make a conversion
different.
In Java:In Objective-C:

21. Categories
 Category is the best way to add more methods to class in objective – C language.
 We can override method in base class but it is poor programming practice( duplicate functionalities of
method when running time).
 Name of category start with base class plus category name( BaseClassName+CategoryName) in import
section.
class
Category

22. Categories
 Syntax:
@interface ClassName (CategoryName)
//// methods declaration part
@end

23. Categories
Cateories Example:
 MyModel class has only one method (ownMethod).

24. Categories
Cateories Example:
 CategoryOfMyModel has one method (newMethod).

25. Categories
Cateories Example:
MyModel
-(void)ownMethod
-(void)newMethod
Compile time
MyModel
-(void)ownMethod
MyModel+Categor
yModel
-(void)newMethod

26. Class Extensions
• Class extension is a special case allows creating a category without a name
- when you define an unnamed category like this, you can extend the class by adding
additional instance variables and properties.
- This is not allowed for named categories.

27. Class Extensions Cont......
MyClass.h
MyClass.m

28. Class Extensions Count......
Main method

29. Protocol
• protocol fully complete abstraction every method in protocol is abstract
• it is list the method name without body, it wait other class implement it and implement
body to it.
• we use it to create the standard method for all classes use the same method when they
implement protocol, it is look like interface in java.
• and it use for delegate also
syntax in objective c syntax in java

30. Protocol
• in objective divided two part of protocol @required and @optional
• @required it mean that we need to implement method when the class implements it.
• @optional it mean that we are not need to implement method when the class
implements it, it is up to you.
syntax:

31. Protocol
• we can implement more than one protocol
• how to implement single and multiple implement protocol
• first we need to import protocol
single implementation in objective c Single implementation in java

32. Protocol
multiple implementation in objective c multiple implementation in java

33. Delegate
• Delegate allow one object send message to other object when an event happen
• We use delegate almost for event handler in IOS
• We can use delegate when we want it to do something when something happen in our
program and raise it up.
• We almost use id for create a delegate
• We will raise it detail in later chapter that detail about the delegate

34. Composite Object
• What is composite object?
 A technique that a class consists of one ore more objects from other classes is call
“Composite Object”.
 Diagram above show you that ClassA has ClassB as its composite.
 If ClassA is deleted then ClassB is also deleted as a result. But if ClassB is deleted ClassA will
not be delete.
ClassA ClassB

35. Composite Object
• Example of composite object:

36. Composite Object
• Let Create other Square class that have Rectangle as its composite

37. Composite Object
• In our main.m file

38. Composition Object
• Let compare our code with java code:
 Rectangle.java

39. Composite Object
• Square.java

40. Composite Object
• Main.java

41. Composite Object
• The result of these two will output the same

42. Thank you