**Course Title:** Mastering TypeScript: From Basics to Advanced Applications **Section Title:** Classes and Object-Oriented Programming **Topic:** Build a class-based system that demonstrates inheritance and interfaces.(Lab topic) **Introduction** In the previous topics, we have covered the basics of classes and object-oriented programming in TypeScript. We have learned about classes, constructors, inheritance, access modifiers, and interfaces. Now, it's time to put this knowledge into practice by building a class-based system that demonstrates inheritance and interfaces. **Lab Overview** In this lab, we will build a simple class-based system that models a university. We will define classes for `University`, `Department`, `Course`, and `Student`. We will use inheritance to create a hierarchical structure of classes, where `Department` and `Student` inherit from `University`. We will also use interfaces to define a contract for classes that can be used to calculate the total number of students. **Step 1: Define Interfaces** First, let's define two interfaces, `UniversityInterface` and `StudentInterface`. These interfaces will define the properties and methods that must be implemented by classes that implement them. ```typescript // university-interface.ts interface UniversityInterface { name: string; location: string; } // student-interface.ts interface StudentInterface { id: number; name: string; calculateGpa(): number; } ``` **Step 2: Define University Class** Next, let's define the `University` class, which will inherit from `UniversityInterface`. ```typescript // university.ts class University implements UniversityInterface { name: string; location: string; constructor(name: string, location: string) { this.name = name; this.location = location; } } ``` **Step 3: Define Department Class** Now, let's define the `Department` class, which will inherit from `University` and implement the `StudentInterface`. ```typescript // department.ts class Department extends University implements StudentInterface { departmentName: string; students: Student[]; constructor(name: string, location: string, departmentName: string) { super(name, location); this.departmentName = departmentName; this.students = []; } addStudent(student: Student) { this.students.push(student); } } ``` **Step 4: Define Course Class** Next, let's define the `Course` class. ```typescript // course.ts class Course { courseName: string; creditHours: number; constructor(courseName: string, creditHours: number) { this.courseName = courseName; this.creditHours = creditHours; } } ``` **Step 5: Define Student Class** Now, let's define the `Student` class, which will implement the `StudentInterface`. ```typescript // student.ts class Student implements StudentInterface { id: number; name: string; courses: Course[]; constructor(id: number, name: string) { this.id = id; this.name = name; this.courses = []; } addCourse(course: Course) { this.courses.push(course); } calculateGpa(): number { // implement GPA calculation logic here return 3.5; } } ``` **Conclusion** In this lab, we have demonstrated the use of inheritance and interfaces in building a class-based system in TypeScript. We have defined classes for `University`, `Department`, `Course`, and `Student`, and used interfaces to define contracts for classes. **Key Takeaways** * Inheritance allows us to create a hierarchical structure of classes, where subclasses inherit properties and methods from parent classes. * Interfaces define contracts for classes, specifying properties and methods that must be implemented. * Interfaces can be used to ensure that classes implement specific functionality. **Further Learning** If you want to learn more about interfaces and inheritance in TypeScript, please visit the official TypeScript documentation at [https://www.typescriptlang.org/docs/](https://www.typescriptlang.org/docs/). **Do You Have Any Questions?** Please leave your questions or comments below.

// university-interface.ts
interface UniversityInterface {
  name: string;
  location: string;
}

// student-interface.ts
interface StudentInterface {
  id: number;
  name: string;
  calculateGpa(): number;
}

// university.ts
class University implements UniversityInterface {
  name: string;
  location: string;

  constructor(name: string, location: string) {
    this.name = name;
    this.location = location;
  }
}

// department.ts
class Department extends University implements StudentInterface {
  departmentName: string;
  students: Student[];

  constructor(name: string, location: string, departmentName: string) {
    super(name, location);
    this.departmentName = departmentName;
    this.students = [];
  }

  addStudent(student: Student) {
    this.students.push(student);
  }
}

// course.ts
class Course {
  courseName: string;
  creditHours: number;

  constructor(courseName: string, creditHours: number) {
    this.courseName = courseName;
    this.creditHours = creditHours;
  }
}

// student.ts
class Student implements StudentInterface {
  id: number;
  name: string;
  courses: Course[];

  constructor(id: number, name: string) {
    this.id = id;
    this.name = name;
    this.courses = [];
  }

  addCourse(course: Course) {
    this.courses.push(course);
  }

  calculateGpa(): number {
    // implement GPA calculation logic here
    return 3.5;
  }
}