OOPS

Object Relations

Handling object relationships within code:

Relation	Handling
Aggregation	References
Composition	References
Generalization	Abstraction
Realization	Interface

Relations may also be:

• one-to-one uni-directional
• one-to-one bi-directional
• one-to-many uni-directional
• one-to-many bi-directional

Bank and Customers are a good example of one-to-many relationship.

S.O.L.I.D. Principles

• S - Single-responsiblity Principle
• O - Open-closed Principle
• L - Liskov Substitution Principle
• I - Interface Segregation Principle
• D - Dependency Inversion Principle

https://www.digitalocean.com/community/conceptual_articles/s-o-l-i-d-the-first-five-principles-of-object-oriented-design

Example: School & Department

Tightly-Coupled & One-To-One. Both objects have strong dependency on one another.

class School {
  private Department d;

  School() {
    d = new Department(this);
  }

  // Public getter.
  public Department getDepartment() {
    return d;
  }
}

class Department {
  // Keeps reference to that particular School instance.
  private School s;

  // Take reference.
  Department(School school) {
    s = school;
  }

  // Public getter.
  public School getSchool() {
    return s;
  }
}