Association – Relations Between Objects And Classes

To pick up where we left off our Class/ Object Relations discussion, we are going to continue with Association. 

Association

We are speaking of an Association when one object, say Object B uses or has an interaction with Object A. There may be cases where Object B interacts with Object A and vice versa. In such a scenario we are dealing with a Bidirectional Association.

Note: Association is used to represent fields (constants, variables) in a class

One Way Association
Teacher Object Knows About Student Object
Class Teacher Depends On Class Student

Bi-directional Association
Teacher Object Knows About Student Object
Class Teacher Depends On Class Student

Student Object Knows About Teacher Object
Class Student Depends On Class Teacher

Disclaimer: The following code examples display combined example of Dependency and Association trying to solidify your understanding of the difference between those topics.

Pseudo Code
//Course Class
class Course is
courseTitle: String

method constructor(String courseTitle) is
this.courseTitle = courseTitle

method courseId(): String is
return this.courseTitle

//Student Class
class Student is
name: String 
lastName: String
age: Integer

method constructor(String name, String lastName, Integer age) is
this.name = name
this.latsName = lastName
this.age = age

method knows(Course course): String is //Student has a Dependency with class Course
print(course.courseId())

//Teacher Class
class Teacher is

//class Teacher has an association with class Student
//A Teacher object knows about Student Objects
//class Professor depends on class Student
private students: Student //Association

method examen(Course course) is //Professor has a Dependency with class Course
this.student.knows(course)

Swift Code

import Foundation

class Course {

    private var courseTitle: String

    init( _ courseTitle: String) {
        self.courseTitle = courseTitle
    }
    
    func courseId() -> String {
        return courseTitle
    }
}

class Student {
    
    let name: String
    let lastName: String
    let age: Int
    
    init(name: String, lastName: String, age: Int) {
        self.name = name
        self.lastName = lastName
        self.age = age
    }

    func knows( _ course: Course) { //Dependency
        print(course.courseId())
    }
    
}
// Teacher ––––––––> Student
class Teacher {
    //class Teacher has an association with class Student
    //A Teacher object knows about Student Objects
    //class Professor depends on class Student
    
    private var student: Student //Association

    init( _ student: Student) {
        self.student = student
    }
    
    func examen( _ course: Course ) { //Dependency
        self.student.knows(course)
    }
}


let newStudent = Student(name: "Joseph", lastName: "Doe", age: 24)
let teacher = Teacher(newStudent)
let course = Course("Algebra")
teacher.examen(course) //Algebra