Association and Aggregation

Association

Association is a has-a relationship between two classes. It represents a more general relationship where one class is connected to another but not necessarily in a strong way.

Example:

Suppose we have two classes, Teacher and Student , and there is an association between them

Below is the implementation of the above example:

C++

#include <iostream>
#include <vector>
 
class Student {
public:
    Student(std::string name)
        : name(name)
    {
    }
 
    std::string getName() const { return name; }
 
private:
    std::string name;
};
 
class Teacher {
public:
    Teacher(std::string name)
        : name(name)
    {
    }
 
    void addStudent(const Student& student)
    {
        students.push_back(student);
    }
 
    void listStudents()
    {
        std::cout << name << " teaches: ";
        for (const Student& student : students) {
            std::cout << student.getName() << " ";
        }
        std::cout << std::endl;
    }
 
private:
    std::string name;
    std::vector<Student> students;
};
 
int main()
{
    Teacher mathTeacher("Mr. Smith");
    Student alice("Alice");
    Student bob("Bob");
 
    mathTeacher.addStudent(alice);
    mathTeacher.addStudent(bob);
 
    mathTeacher.listStudents();
 
    return 0;
}

Output

Mr. Smith teaches: Alice Bob

In this example:

Teacher and Student are two classes representing a teacher and a student respectively.
The Teacher class has a method addStudent to associate students with a teacher.
An association is created by adding students to the teacher’s list.

Aggregation

Aggregation is a type of association that represnets a whole-part relationship. It implies that one one class (the whole) contians or is composed of another class (the part). Aggregation is often depicted as a diamond-shape arrow.

Let’s modify the previous example to demonstrate aggregation:

C++

#include <iostream>
#include <vector>
 
class Student {
public:
    Student(std::string name)
        : name(name)
    {
    }
 
    std::string getName() const { return name; }
 
private:
    std::string name;
};
 
class School {
public:
    School(std::string name)
        : name(name)
    {
    }
 
    void addStudent(const Student& student)
    {
        students.push_back(student);
    }
 
    void listStudents()
    {
        std::cout << "Students at " << name << ": ";
        for (const Student& student : students) {
            std::cout << student.getName() << " ";
        }
        std::cout << std::endl;
    }
 
private:
    std::string name;
    std::vector<Student> students;
};
 
int main()
{
    School mySchool("XYZ School");
    Student alice("Alice");
    Student bob("Bob");
 
    mySchool.addStudent(alice);
    mySchool.addStudent(bob);
 
    mySchool.listStudents();
 
    return 0;
}

Output

Students at XYZ School: Alice Bob

In this updated example:

We introduced a School class, which contains a list of students. This represents an aggregation, where a school is composed of students.

Object Model | Object Oriented Analysis & Design

Object-Oriented Programming (OOP) is a fundamental paradigm in modern software development that has transformed the way we design, build, and maintain software systems. OOP is centered around the concept of objects, which are self-contained, reusable units that encapsulate both data and the operations that can be performed on that data. This approach mirrors real-world modeling, making it easier to understand, manage, and expand software projects.

Important Topics for the Object Model

Objects and Classes
Encapsulation and Data Hiding
Message Passing
Inheritance
Polymorphism
Generalization and Specialization
Association and Aggregation
Benefits of Object Model
Conclusion

Association and Aggregation

Association

C++

Aggregation

C++

Object Model | Object Oriented Analysis & Design

Similar Reads

Contact Us