Experiment 2.1: Data Structures, Collections, and Multithreading

Problem statement: Create a Java program to maintain employee records using an ArrayList. The program should allow the user to add, update, remove, search, and display employees.

Algorithm

1. Create an Employee class with id, name, department, salary, update, and display methods.
2. Create an ArrayList to store employee objects.
3. Display a menu for add, update, remove, search, display, and exit.
4. For add, read details and reject duplicate employee ids.
5. For update, remove, and search, first locate the employee by id.
6. Repeat the menu until the user enters 0.

Java Program

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

class Employee {
    private int id;
    private String name;
    private String department;
    private double salary;

    public Employee(int id, String name, String department, double salary) {
        this.id = id;
        this.name = name;
        this.department = department;
        this.salary = salary;
    }

    public int getId() {
        return id;
    }

    public void update(String name, String department, double salary) {
        this.name = name;
        this.department = department;
        this.salary = salary;
    }

    public void display() {
        System.out.printf("%-6d %-15s %-12s %.2f%n", id, name, department, salary);
    }
}

public class EmployeeArrayListSystem {
    private static Employee findEmployee(List<Employee> employees, int id) {
        for (Employee employee : employees) {
            if (employee.getId() == id) {
                return employee;
            }
        }
        return null;
    }

    private static void addEmployee(List<Employee> employees, Scanner scanner) {
        System.out.print("Enter id: ");
        int id = Integer.parseInt(scanner.nextLine().trim());

        if (findEmployee(employees, id) != null) {
            System.out.println("Employee id already exists.");
            return;
        }

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

        System.out.print("Enter department: ");
        String department = scanner.nextLine().trim();

        System.out.print("Enter salary: ");
        double salary = Double.parseDouble(scanner.nextLine().trim());

        employees.add(new Employee(id, name, department, salary));
        System.out.println("Employee added.");
    }

    private static void updateEmployee(List<Employee> employees, Scanner scanner) {
        System.out.print("Enter id to update: ");
        int id = Integer.parseInt(scanner.nextLine().trim());
        Employee employee = findEmployee(employees, id);

        if (employee == null) {
            System.out.println("Employee not found.");
            return;
        }

        System.out.print("Enter new name: ");
        String name = scanner.nextLine().trim();

        System.out.print("Enter new department: ");
        String department = scanner.nextLine().trim();

        System.out.print("Enter new salary: ");
        double salary = Double.parseDouble(scanner.nextLine().trim());

        employee.update(name, department, salary);
        System.out.println("Employee updated.");
    }

    private static void removeEmployee(List<Employee> employees, Scanner scanner) {
        System.out.print("Enter id to remove: ");
        int id = Integer.parseInt(scanner.nextLine().trim());
        Employee employee = findEmployee(employees, id);

        if (employee == null) {
            System.out.println("Employee not found.");
            return;
        }

        employees.remove(employee);
        System.out.println("Employee removed.");
    }

    private static void searchEmployee(List<Employee> employees, Scanner scanner) {
        System.out.print("Enter id to search: ");
        int id = Integer.parseInt(scanner.nextLine().trim());
        Employee employee = findEmployee(employees, id);

        if (employee == null) {
            System.out.println("Employee not found.");
        } else {
            System.out.println("ID     Name            Department   Salary");
            employee.display();
        }
    }

    private static void displayEmployees(List<Employee> employees) {
        if (employees.isEmpty()) {
            System.out.println("No employee records available.");
            return;
        }

        System.out.println("ID     Name            Department   Salary");
        for (Employee employee : employees) {
            employee.display();
        }
    }

    public static void main(String[] args) {
        List<Employee> employees = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        try {
            int choice;
            do {
                System.out.println("\n1. Add  2. Update  3. Remove  4. Search  5. Display  0. Exit");
                System.out.print("Enter choice: ");
                choice = Integer.parseInt(scanner.nextLine().trim());

                switch (choice) {
                    case 1 -> addEmployee(employees, scanner);
                    case 2 -> updateEmployee(employees, scanner);
                    case 3 -> removeEmployee(employees, scanner);
                    case 4 -> searchEmployee(employees, scanner);
                    case 5 -> displayEmployees(employees);
                    case 0 -> System.out.println("Program ended.");
                    default -> System.out.println("Invalid choice.");
                }
            } while (choice != 0);
        } finally {
            scanner.close();
        }
    }
}

Sample Output

1. Add  2. Update  3. Remove  4. Search  5. Display  0. Exit
Enter choice: 1
Enter id: 101
Enter name: Anaya
Enter department: HR
Enter salary: 45000
Employee added.

1. Add  2. Update  3. Remove  4. Search  5. Display  0. Exit
Enter choice: 4
Enter id to search: 101
ID     Name            Department   Salary
101    Anaya           HR           45000.00

Problem statement: Create a Java program that stores cards in a Collection and displays all cards matching a symbol entered by the user.

Algorithm

1. Create a Card class with symbol and value.
2. Declare Collection<Card> cards = new ArrayList<>().
3. Read the number of cards and add every card to the collection.
4. Read the symbol to be searched.
5. Traverse the collection and copy matching cards to another collection.
6. Display matching cards or print a no-match message.

Java Program

import java.util.ArrayList;
import java.util.Collection;
import java.util.Scanner;

class Card {
    private final String symbol;
    private final String value;

    public Card(String symbol, String value) {
        this.symbol = symbol;
        this.value = value;
    }

    public String getSymbol() {
        return symbol;
    }

    public void display() {
        System.out.println(symbol + " - " + value);
    }
}

public class CardCollectionLookup {
    private static Collection<Card> findCardsBySymbol(Collection<Card> cards, String symbol) {
        Collection<Card> matchingCards = new ArrayList<>();

        for (Card card : cards) {
            if (card.getSymbol().equalsIgnoreCase(symbol)) {
                matchingCards.add(card);
            }
        }

        return matchingCards;
    }

    public static void main(String[] args) {
        Collection<Card> cards = new ArrayList<>();
        Scanner scanner = new Scanner(System.in);

        try {
            System.out.print("Enter number of cards: ");
            int count = Integer.parseInt(scanner.nextLine().trim());

            for (int i = 1; i <= count; i++) {
                System.out.println("Card " + i);
                System.out.print("Enter symbol: ");
                String symbol = scanner.nextLine().trim();

                System.out.print("Enter value: ");
                String value = scanner.nextLine().trim();

                cards.add(new Card(symbol, value));
            }

            System.out.print("Enter symbol to search: ");
            String requiredSymbol = scanner.nextLine().trim();

            Collection<Card> result = findCardsBySymbol(cards, requiredSymbol);

            if (result.isEmpty()) {
                System.out.println("No cards found for symbol " + requiredSymbol + ".");
            } else {
                System.out.println("Cards with symbol " + requiredSymbol + ":");
                for (Card card : result) {
                    card.display();
                }
            }
        } finally {
            scanner.close();
        }
    }
}

Sample Output

Enter number of cards: 4
Card 1
Enter symbol: Heart
Enter value: Ace
Card 2
Enter symbol: Spade
Enter value: King
Card 3
Enter symbol: Heart
Enter value: 10
Card 4
Enter symbol: Diamond
Enter value: Queen
Enter symbol to search: Heart
Cards with symbol Heart:
Heart - Ace
Heart - 10

Problem statement: Create a ticket booking program where multiple threads try to book tickets from one shared counter. Use synchronization so tickets are not oversold, and assign priorities to booking threads.

Algorithm

1. Create a TicketCounter class with availableTickets.
2. Write synchronized bookTickets to check availability and subtract tickets in one protected block.
3. Create BookingThread by extending Thread.
4. Store passenger name and requested tickets in each thread object.
5. Set thread names and priorities through the constructor.
6. Start all booking threads and call join() so the main thread waits for completion.

Java Program

class TicketCounter {
    private int availableTickets;

    public TicketCounter(int availableTickets) {
        this.availableTickets = availableTickets;
    }

    public synchronized void bookTickets(String passengerName, int requestedTickets) {
        String threadName = Thread.currentThread().getName();
        System.out.println(threadName + " processing request for " + passengerName);

        if (requestedTickets <= availableTickets) {
            availableTickets -= requestedTickets;
            System.out.println(passengerName + " booked " + requestedTickets
                    + " ticket(s). Remaining tickets: " + availableTickets);
        } else {
            System.out.println(passengerName + " could not book " + requestedTickets
                    + " ticket(s). Only " + availableTickets + " left.");
        }
    }
}

class BookingThread extends Thread {
    private final TicketCounter counter;
    private final String passengerName;
    private final int requestedTickets;

    public BookingThread(TicketCounter counter, String passengerName,
                         int requestedTickets, int priority) {
        this.counter = counter;
        this.passengerName = passengerName;
        this.requestedTickets = requestedTickets;
        setName(passengerName + "-thread");
        setPriority(priority);
    }

    @Override
    public void run() {
        counter.bookTickets(passengerName, requestedTickets);
    }
}

public class TicketBookingSystem {
    public static void main(String[] args) throws InterruptedException {
        TicketCounter counter = new TicketCounter(5);

        BookingThread vip = new BookingThread(counter, "Ananya", 2, Thread.MAX_PRIORITY);
        BookingThread regular = new BookingThread(counter, "Ravi", 3, Thread.NORM_PRIORITY);
        BookingThread waiting = new BookingThread(counter, "Meera", 2, Thread.MIN_PRIORITY);

        vip.start();
        regular.start();
        waiting.start();

        vip.join();
        regular.join();
        waiting.join();

        System.out.println("All booking requests processed.");
    }
}

Sample Output

The exact order can vary because thread scheduling is controlled by the JVM and operating system.

Ananya-thread processing request for Ananya
Ananya booked 2 ticket(s). Remaining tickets: 3
Ravi-thread processing request for Ravi
Ravi booked 3 ticket(s). Remaining tickets: 0
Meera-thread processing request for Meera
Meera could not book 2 ticket(s). Only 0 left.
All booking requests processed.