Objective-C Header and Class Implementation

Person.h

#import <Foundation/Foundation.h>

@interface Person:NSObject{

   NSString *name;

   int age;

}

- (NSString *)name;

- (void) setName: (NSString *) newName;

- (int)age;

- (void) setAge: (int) newAge;

//actions

- (BOOL) isAllowedToVote;

- (void castBallot;

@end

Person.m

#import "Person.h"

@implementation Person

- (int) age{

   return age;

}

- (void) setAge: (int) value{

   age = value;

}

//... and other methods

@end

Using a class

id anObject = [[SomeClass alloc] init];

- (id) init

{

   self = [super init];

   if(self){

     //initializations

   }

   return self;

}

- (Person *) createPersonWithName: (NSString *) aName{

   Person *aPerson = [[Person alloc] init];

   [aPerson setName:aName];

   [aPerson setAge:21];

   return aPerson;

}

Class Inheritance

@interface Student : Person {

   NSString *major;

}

@end

@implementation Student

// Constructor for a student

- (id) init

{

   self = [super init];

   if(self != nil){

      //set attributes

      [self setMajor:@"Undefined"];

   }

   return self;

}

@end

Objective-C Selector

id object;
SEL anAction = @selector(action:);
if([object respondsToSelector:anAction]){
   [object performSelector:anAction withObject:self];
}

Objective-C Object Messaging

[receiver message]
[receiver message:argument]
[receiver message:arg1 argument2:arg2]
int status = [receiver message];
[receiver makeGroup:group, memberOne, memberTwo, memberThree];

[rectangle draw]
[rectangle setColor:blue]
[rectangle setStrokeColor:blue andThickness:2.0]
double length = [rectangle circumference];
[NSArray arrayWithObjects:one, two, three, nil];

Java vs. Objective-C

Java
Rectangle rect = Rectangle(someWidth, someHeight);
println(rect.getHeight());
boolean inside = rect.contains(x,y);

Objective-C
Rectangle *rect = [[Rectangle alloc] initWithWidth:someWidth andHeight:someHeight];
NSLog(@"%f", [rect height]);
BOOL inside = [rect containsPointWithX:x andY:y]

Objective-C Identiy vs. Equality

// test for object identity:
BOOL identical = @"Peter" == @"Peter";     //YES
            identical = @"Peter" == @" Peter ";    //NO

// test for string equality: will return YES
NSString *aName = @"Peter";
NSMutableString *anotherName = [NSMutableString stringWithString:@"P"];

[anotherName appendString:@"eter"];

BOOL same = [aName isEqualToString:anotherName];     //YES
BOOL equal = (aName == anotherName);         //NO

// test for existence
BOOL exists = (object != nil);