Experiment 1.2: Product Management, Library System, and Student Information System

Java - What is OOP?

OOP stands for Object-Oriented Programming.

Procedural programming is about writing procedures or methods that perform operations on the data, while object-oriented programming is about creating objects that contain both data and methods.

Object-oriented programming has several advantages over procedural programming:

• OOP is faster and easier to execute.
• OOP provides a clear structure for the programs.
• OOP helps to keep the Java code DRY - "Don't Repeat Yourself" - and makes the code easier to maintain, modify, and debug.
• OOP makes it possible to create full reusable applications with less code and shorter development time.

Java - What are Classes and Objects?

Classes and objects are the two main aspects of object-oriented programming.

A class is a template for objects, and an object is an instance of a class. When the individual objects are created, they inherit all the variables and methods from the class.

Java Inheritance (Subclass and Superclass)

In Java, it is possible to inherit attributes and methods from one class to another. We group the "inheritance concept" into two categories:

• Subclass (child) - the class that inherits from another class.
• Superclass (parent) - the class being inherited from.

To inherit from a class, use the extends keyword. In the example below, the Car class (subclass) inherits the attributes and methods from the Vehicle class (superclass):

class Vehicle {
    protected String brand = "Ford";  // Vehicle attribute

    public void honk() {              // Vehicle method
        System.out.println("Tuut, tuut!");
    }
}

class Car extends Vehicle {
    private String modelName = "Mustang";  // Car attribute

    public static void main(String[] args) {
        // Create a myCar object
        Car myCar = new Car();

        // Call the honk() method (from the Vehicle class) on the myCar object
        myCar.honk();

        // Display the brand attribute (from the Vehicle class)
        // and the modelName attribute (from the Car class)
        System.out.println(myCar.brand + " " + myCar.modelName);
    }
}

Experiment 1.1 used one class as a container for main. This experiment is where object-oriented programming actually starts: every task is modelled as classes first, and main only creates objects and calls their methods. Revise these ideas before writing any code.

class Product { /* fields + methods */ }

Product p1 = new Product(101, "Mouse", 799.5);
Product p2 = new Product(102, "Keyboard", 1499.0);

public Product(int id, String name, double price) {
    this.id = id;        // field = parameter
    this.name = name;
    this.price = price;
}

private double price;               // hidden data
public void displayProductDetails() // controlled access
{ ... }

class Fiction extends Book {
    public Fiction(String title, String author, double price) {
        super(title, author, price); // run Book's constructor first
    }
}

class Book {
    protected String title;   // Fiction and NonFiction can use it
    protected String author;
    protected double price;
}

Book b = new Fiction("The Guide", "R. K. Narayan", 350);
b.displayDetails();   // Fiction's version runs, not Book's

abstract class Person {
    public abstract void displayDetails(); // no body here
}
// new Person(...)  -> compile error

class Library {
    private Book[] shelf;   // a Library HAS-A collection of Books
}

Problem statement: Write a Java program to create a Product class with attributes id, name, and price. The program should demonstrate the use of constructors and methods to display product details.

Algorithm

1. Start the program and create a Scanner object.
2. Read the product ID with nextInt(), then consume the leftover newline with nextLine().
3. Read the product name with nextLine() so names with spaces work.
4. Read the product price with nextDouble().
5. Create a Product object - the constructor copies the three values into the private fields.
6. Call displayProductDetails() to print the ID, name, and price.
7. Close the scanner and end the program.

Java Program

import java.util.Scanner;

class Product {
    // Attributes
    private int id;
    private String name;
    private double price;

    // Constructor to initialise Product
    public Product(int id, String name, double price) {
        this.id = id;
        this.name = name;
        this.price = price;
    }

    // Method to display product details
    public void displayProductDetails() {
        System.out.println("\nProduct Details:");
        System.out.println("ID: " + id);
        System.out.println("Name: " + name);
        System.out.println("Price: Rs." + price);
    }
}

public class ProductDemo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Taking product details from the user
        System.out.print("Enter Product ID: ");
        int id = scanner.nextInt();
        scanner.nextLine(); // Consume newline

        System.out.print("Enter Product Name: ");
        String name = scanner.nextLine();

        System.out.print("Enter Product Price: Rs.");
        double price = scanner.nextDouble();

        // Creating Product object
        Product product = new Product(id, name, price);

        // Displaying product details
        product.displayProductDetails();

        scanner.close();
    }
}

Sample Output

Enter Product ID: 101
Enter Product Name: Wireless Mouse
Enter Product Price: Rs.799.5

Product Details:
ID: 101
Name: Wireless Mouse
Price: Rs.799.5

Problem statement: Write a Java program to implement a library management system. The program should use a base class Book and derived classes Fiction and NonFiction.

Algorithm

1. Read the type, title, author, and price for the first book.
2. Create a Fiction or NonFiction object based on the type and store it in a Book reference.
3. Consume the leftover newline, then repeat both steps for the second book.
4. Call displayDetails() on both references - the overridden subclass version runs (runtime polymorphism).
5. Inside each override, print the heading, then call super.displayDetails() for the common fields.

Java Program

import java.util.Scanner;

// Base class: Book
class Book {
    protected String title;
    protected String author;
    protected double price;

    // Constructor
    public Book(String title, String author, double price) {
        this.title = title;
        this.author = author;
        this.price = price;
    }

    // Method to display book details (overridden in derived classes)
    public void displayDetails() {
        System.out.println("Title: " + title);
        System.out.println("Author: " + author);
        System.out.println("Price: Rs." + price);
    }
}

// Derived class: Fiction
class Fiction extends Book {
    public Fiction(String title, String author, double price) {
        super(title, author, price);
    }

    // @Override is an annotation, not code: it asks the compiler to verify
    // that this method really overrides Book's displayDetails()
    @Override
    public void displayDetails() {
        System.out.println("\nFiction Book Details:");
        super.displayDetails();
    }
}

// Derived class: NonFiction
class NonFiction extends Book {
    public NonFiction(String title, String author, double price) {
        super(title, author, price);
    }

    // @Override annotation again: compiler-checked override
    @Override
    public void displayDetails() {
        System.out.println("\nNon-Fiction Book Details:");
        super.displayDetails();
    }
}

public class LibraryManagementSystem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Taking input for the first book
        System.out.println("Book 1:");
        System.out.print("Type (Fiction/Non-Fiction): ");
        String type1 = scanner.nextLine();

        System.out.print("Title: ");
        String title1 = scanner.nextLine();

        System.out.print("Author: ");
        String author1 = scanner.nextLine();

        System.out.print("Price: Rs.");
        double price1 = scanner.nextDouble();
        scanner.nextLine(); // Consume newline

        // Creating object based on type
        Book book1 = (type1.equalsIgnoreCase("Fiction"))
                ? new Fiction(title1, author1, price1)
                : new NonFiction(title1, author1, price1);

        // Taking input for the second book
        System.out.println("\nBook 2:");
        System.out.print("Type (Fiction/Non-Fiction): ");
        String type2 = scanner.nextLine();

        System.out.print("Title: ");
        String title2 = scanner.nextLine();

        System.out.print("Author: ");
        String author2 = scanner.nextLine();

        System.out.print("Price: Rs.");
        double price2 = scanner.nextDouble();

        // Creating object based on type
        Book book2 = (type2.equalsIgnoreCase("Fiction"))
                ? new Fiction(title2, author2, price2)
                : new NonFiction(title2, author2, price2);

        // Displaying book details
        book1.displayDetails();
        book2.displayDetails();

        scanner.close();
    }
}

Sample Output

Book 1:
Type (Fiction/Non-Fiction): Fiction
Title: The Guide
Author: R. K. Narayan
Price: Rs.350

Book 2:
Type (Fiction/Non-Fiction): Non-Fiction
Title: Wings of Fire
Author: A. P. J. Abdul Kalam
Price: Rs.450

Fiction Book Details:
Title: The Guide
Author: R. K. Narayan
Price: Rs.350.0

Non-Fiction Book Details:
Title: Wings of Fire
Author: A. P. J. Abdul Kalam
Price: Rs.450.0

Problem statement: Design a student information system using Java with the following features: use an abstract class Person with attributes name, age, and methods like displayDetails(). Create derived classes Student and Teacher to override displayDetails() and add unique attributes like rollNumber for students and subject for teachers.

Algorithm

1. Read the student's name, age, and roll number; consume the leftover newline after the numeric reads.
2. Create a Student object - its constructor calls super(name, age), then stores rollNumber.
3. Read the teacher's name, age, and subject the same way.
4. Create a Teacher object - its constructor calls super(name, age), then stores subject.
5. Call displayDetails() on each object - the subclass implementation runs.
6. Note that Person itself is never instantiated; it only defines the shared state and the contract.

Java Program

import java.util.Scanner;

// Abstract class Person
abstract class Person {
    protected String name;
    protected int age;

    // Constructor
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // Abstract method to be overridden by derived classes
    public abstract void displayDetails();
}

// Derived class Student
class Student extends Person {
    private int rollNumber;

    // Constructor
    public Student(String name, int age, int rollNumber) {
        super(name, age);
        this.rollNumber = rollNumber;
    }

    // Overriding displayDetails method
    // (@Override is an annotation - a compile-time check, not runtime code)
    @Override
    public void displayDetails() {
        System.out.println("\nStudent Details:");
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Roll Number: " + rollNumber);
    }
}

// Derived class Teacher
class Teacher extends Person {
    private String subject;

    // Constructor
    public Teacher(String name, int age, String subject) {
        super(name, age);
        this.subject = subject;
    }

    // Overriding displayDetails method
    @Override
    public void displayDetails() {
        System.out.println("\nTeacher Details:");
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
        System.out.println("Subject: " + subject);
    }
}

public class StudentInformationSystem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Input for Student
        System.out.println("Add Student:");
        System.out.print("Name: ");
        String studentName = scanner.nextLine();

        System.out.print("Age: ");
        int studentAge = scanner.nextInt();

        System.out.print("Roll Number: ");
        int rollNumber = scanner.nextInt();
        scanner.nextLine(); // Consume newline

        Student student = new Student(studentName, studentAge, rollNumber);

        // Input for Teacher
        System.out.println("\nAdd Teacher:");
        System.out.print("Name: ");
        String teacherName = scanner.nextLine();

        System.out.print("Age: ");
        int teacherAge = scanner.nextInt();
        scanner.nextLine(); // Consume newline

        System.out.print("Subject: ");
        String subject = scanner.nextLine();

        Teacher teacher = new Teacher(teacherName, teacherAge, subject);

        // Display details
        student.displayDetails();
        teacher.displayDetails();

        scanner.close();
    }
}

Sample Output

Add Student:
Name: Aman Kumar
Age: 19
Roll Number: 1101

Add Teacher:
Name: Neha Sharma
Age: 38
Subject: Java Programming

Student Details:
Name: Aman Kumar
Age: 19
Roll Number: 1101

Teacher Details:
Name: Neha Sharma
Age: 38
Subject: Java Programming