OOP Concepts - Part 1 - Encapsulation_Aggregation

Object-oriented Programming Features

Part 1: Encapsulation and Aggregation

Encapsulation

• Definition: A method to hide data, properties, and methods from outside access and only expose necessary components.

• Functionality: Acts as a protective barrier preventing random access to code and data from outside the class.

• Analogy: Similar to a capsule that contains various medicines, encapsulation wraps code and data into a single unit.

Data Hiding

• User Experience: Users are unaware of the inner workings of a class. The implementation details are hidden from them.

• Setter and Getter Methods: Users only interact with the class through setter methods to pass values, which get initialized into variables.

• Benefits:

  • Increased Flexibility: Variables can be made read-only or write-only based on requirements.

  • Reusability: Improved reusability; easier to adapt for new requirements.

  • Testing: Easier to conduct unit testing on encapsulated code.

Access Modifiers

• Public: Accessible everywhere, has the widest access scope among modifiers.

• Protected: Accessible within the package and outside only through inheritance.

• Private: Accessible only within the class itself.

• Default: If no modifier is used, it’s only accessible within the package (default access).

Access Modifier Accessibility Summary

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Implementing Encapsulation in Java

• Steps:

  • Declare class variables as private.

  • Provide public setter and getter methods to modify and view the variables' values.

Aggregation

• Definition: A special form of association that is unidirectional, also referred to as a "has-a" relationship.

• Purpose: Enables an object to be composed of other objects, forming a whole.

• Example: A person consists of a head object, a body object, and two hand objects, among others.

Aggregation in Code

public class Person {
    public Name name;

    public Person(Name name) {
        this.name = name;
    }
}

public class Name {
    public String firstname;
    public String lastname;

    public Name(String firstname, String lastname) {
        this.firstname = firstname;
        this.lastname = lastname;
    }
}

public class Test {
    public static void main(String[] args) {
        Person person = new Person(new Name("John", "Snow"));
        System.out.println("Hello, " + person.name.firstname);
    }
}

Getter and Setter Methods Getter and setter methods are used to access and modify private variables in a class.

• Getter Method: A method that retrieves the value of a private variable. It provides read access to the variable.

• Setter Method: A method that allows for setting or updating the value of a private variable. It provides write access to the variable.

Functionality:

• They help maintain encapsulation by restricting access to the internal state of the object and only allowing it through controlled methods.

• Users can’t directly modify the variables, which helps in validating input data before updating.

Example:

public class Person {  
   private String name;  
   
   // Getter method  
   public String getName() {  
       return name;  
   }  
   
   // Setter method  
   public void setName(String name) {  
       this.name = name;  
   }  
}  

In this example, getName() allows users to access the name variable, while setName(String name) allows users to modify it.