Class Relationships

Tags: #◇Computer Science #◇CCPROG3 #◇Class Relationships #◇Code Snippets #◇M3

◇Key Definitions

Class Relationships describe how various classes and objects interact with each other in an object-oriented system. The primary types are Dependency, Association, Aggregation, and Composition.

◇Theoretical Framework

Dependency (uses-a): A class depends on another if it uses it as a parameter, return type, or local variable. Association (has-a): A broad relationship where all objects have their own lifecycle and there is no owner. Aggregation (has-a): A specialized form of association where there is a whole-part relationship, but the part can exist independently of the whole. Composition (part-of): A strict whole-part relationship where the lifecycle of the part is strictly managed by the whole.

◇Code Implementation

// Dependency
class Printer {
    void print(Document doc) { ... }
}

// Association
class Teacher {
    List<Student> students; // Teacher associates with Students
}

// Aggregation
class Department {
    List<Professor> professors; 
    // Professors can exist without the Department
}

// Composition
class House {
    private Room room; 
    public House() {
        this.room = new Room(); // Room lifecycle bound to House
    }
}

◇Syntax Breakdown

Relationships are typically implemented via fields referencing other classes. Composition uses instantiation within the constructor of the whole to ensure strict lifecycle binding. Aggregation usually passes references via constructors or setters.

◇Complexity Analysis

Establishing relationships does not inherently impact time complexity but increases memory usage (space complexity) due to object references. Proper design minimizes memory leaks and tangled dependencies.

◇References & Navigation

• Previous Topic: ◇Classes and Objects
• Next Topic: ◇Collections
• Related Notes: ◇Overview of Programming Languages