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Encapsulation

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Encapsulation is one of the fundamental principles of Object-Oriented Programming (OOP). It refers to the bundling of data (variables) and methods (functions) that operate on the data into a single unit, typically a class. Encapsulation also involves restricting direct access to some of an object's components, which is a means of preventing accidental interference and misuse of the data.

Key Concepts of Encapsulation

  1. Data Hiding: Encapsulation allows the internal representation of an object to be hidden from the outside. Only the necessary information is exposed through a public interface.
  2. Access Modifiers: Objective-C uses access control keywords to define the visibility of class members. These include @private, @protected, and @public.
  3. Getter and Setter Methods: These methods are used to access and update the value of private variables.

Access Modifiers in Objective-C

  • @private: Members declared as private can only be accessed within the same class.
  • @protected: Members declared as protected can be accessed within the same class and subclasses.
  • @public: Members declared as public can be accessed from any other class.

Example

Let's look at an example to understand encapsulation better.

#import <Foundation/Foundation.h>

@interface Person : NSObject {
    @private
    NSString *name;
    @private
    int age;
}

// Getter and Setter methods
- (void)setName:(NSString *)newName;
- (NSString *)getName;
- (void)setAge:(int)newAge;
- (int)getAge;

@end

@implementation Person

- (void)setName:(NSString *)newName {
    name = newName;
}

- (NSString *)getName {
    return name;
}

- (void)setAge:(int)newAge {
    age = newAge;
}

- (int)getAge {
    return age;
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        Person *person = [[Person alloc] init];
        [person setName:@"John Doe"];
        [person setAge:30];
        
        NSLog(@"Name: %@", [person getName]);
        NSLog(@"Age: %d", [person getAge]);
    }
    return 0;
}

Explanation

  1. Class Definition: The Person class is defined with two private instance variables: name and age.
  2. Getter and Setter Methods: The class provides public methods to set and get the values of these private variables.
  3. Main Function: In the main function, an instance of Person is created, and the getter and setter methods are used to access and modify the private variables.

Practical Exercise

Exercise

Create a class BankAccount with the following specifications:

  • Private instance variables: accountNumber (NSString), balance (double).
  • Public methods to set and get the accountNumber.
  • Public methods to deposit and withdraw money from the account. Ensure that the balance cannot go negative.

Solution

#import <Foundation/Foundation.h>

@interface BankAccount : NSObject {
    @private
    NSString *accountNumber;
    @private
    double balance;
}

- (void)setAccountNumber:(NSString *)newAccountNumber;
- (NSString *)getAccountNumber;
- (void)deposit:(double)amount;
- (BOOL)withdraw:(double)amount;
- (double)getBalance;

@end

@implementation BankAccount

- (void)setAccountNumber:(NSString *)newAccountNumber {
    accountNumber = newAccountNumber;
}

- (NSString *)getAccountNumber {
    return accountNumber;
}

- (void)deposit:(double)amount {
    balance += amount;
}

- (BOOL)withdraw:(double)amount {
    if (balance >= amount) {
        balance -= amount;
        return YES;
    } else {
        NSLog(@"Insufficient funds");
        return NO;
    }
}

- (double)getBalance {
    return balance;
}

@end

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        BankAccount *account = [[BankAccount alloc] init];
        [account setAccountNumber:@"123456789"];
        [account deposit:1000.0];
        
        NSLog(@"Account Number: %@", [account getAccountNumber]);
        NSLog(@"Balance: %.2f", [account getBalance]);
        
        if ([account withdraw:500.0]) {
            NSLog(@"Withdrawal successful");
        } else {
            NSLog(@"Withdrawal failed");
        }
        
        NSLog(@"Balance: %.2f", [account getBalance]);
    }
    return 0;
}

Explanation

  1. Class Definition: The BankAccount class is defined with private instance variables accountNumber and balance.
  2. Getter and Setter Methods: Public methods to set and get the accountNumber are provided.
  3. Deposit and Withdraw Methods: Methods to deposit and withdraw money are implemented. The withdraw method checks if there are sufficient funds before allowing the withdrawal.
  4. Main Function: An instance of BankAccount is created, and the methods are used to manipulate the account.

Summary

Encapsulation is a powerful feature of OOP that helps in data hiding and protecting the internal state of an object. By using access modifiers and getter/setter methods, you can control how the data is accessed and modified. This not only enhances security but also makes the code more maintainable and flexible.

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