Dracula

✅ Question 1 — ShapePkg: Interface with Circle & Rectangle

ShapePkg/ ├── Shape.java (interface) ├── Circle.java (implements Shape) ├── Rectangle.java (implements Shape) └── Main.java (main class) 💻 Code Shape.java javapackage ShapePkg;

public interface Shape { double area(); double perimeter(); } Circle.java javapackage ShapePkg;

public class Circle implements Shape { private double radius;

public Circle(double radius) {
    this.radius = radius;
}

@Override
public double area() {
    return Math.PI * radius * radius;
}

@Override
public double perimeter() {
    return 2 * Math.PI * radius;
}

} Rectangle.java javapackage ShapePkg;

public class Rectangle implements Shape { private double length, width;

public Rectangle(double length, double width) {
    this.length = length;
    this.width = width;
}

@Override
public double area() {
    return length * width;
}

@Override
public double perimeter() {
    return 2 * (length + width);
}

} Main.java javapackage ShapePkg; import java.util.Scanner;

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

    System.out.print("Enter radius of Circle: ");
    double radius = sc.nextDouble();
    Circle c = new Circle(radius);
    System.out.printf("Circle -> Area: %.2f, Perimeter: %.2f%n",
                       c.area(), c.perimeter());

    System.out.print("Enter length of Rectangle: ");
    double length = sc.nextDouble();
    System.out.print("Enter width of Rectangle: ");
    double width = sc.nextDouble();
    Rectangle r = new Rectangle(length, width);
    System.out.printf("Rectangle -> Area: %.2f, Perimeter: %.2f%n",
                       r.area(), r.perimeter());

    sc.close();
}

}

✅ Question 2 — MultiInterfacePkg: Multiple Interface Implementation

💻 Code Printable.java javapackage MultiInterfacePkg;

public interface Printable { void print(); } Showable.java javapackage MultiInterfacePkg;

public interface Showable { void show(); } Document.java javapackage MultiInterfacePkg;

public class Document implements Printable, Showable { private String content;

public Document(String content) {
    this.content = content;
}

@Override
public void print() {
    System.out.println("Printing document: " + content);
}

@Override
public void show() {
    System.out.println("Showing document on screen: " + content);
}

} Main.java javapackage MultiInterfacePkg;

public class Main { public static void main(String[] args) { Document doc = new Document("Java Assignment Report"); doc.print(); doc.show();

    // Polymorphic references
    Printable p = doc;
    p.print();

    Showable s = doc;
    s.show();
}

}

✅ Question 3 — MathOperationsPkg: Calculator with Packages

💻 Code Calculator.java (in MathOperationsPkg) javapackage MathOperationsPkg;

public class Calculator {

public double add(double a, double b) {
    return a + b;
}

public double subtract(double a, double b) {
    return a - b;
}

public double multiply(double a, double b) {
    return a * b;
}

public double divide(double a, double b) {
    if (b == 0) {
        System.out.println("Error: Cannot divide by zero!");
        return 0;
    }
    return a / b;
}

} Main.java (in MainPkg — different package) javapackage MainPkg;

import MathOperationsPkg.Calculator; // explicit import import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); Calculator calc = new Calculator();

    System.out.print("Enter first number: ");
    double a = sc.nextDouble();
    System.out.print("Enter second number: ");
    double b = sc.nextDouble();

    System.out.println("Choose operation: 1-Add  2-Sub  3-Mul  4-Div");
    int choice = sc.nextInt();

    switch (choice) {
        case 1: System.out.println("Result: " + calc.add(a, b)); break;
        case 2: System.out.println("Result: " + calc.subtract(a, b)); break;
        case 3: System.out.println("Result: " + calc.multiply(a, b)); break;
        case 4: System.out.println("Result: " + calc.divide(a, b)); break;
        default: System.out.println("Invalid choice");
    }
    sc.close();
}

}

✅ Question 4 — StudentPkg: Access Modifiers

💻 Code Student.java (in StudentPkg) javapackage StudentPkg;

public class Student { public String name = "Alice"; // accessible everywhere protected int rollNo = 101; // accessible in subclass & same pkg String grade = "A"; // default: same package only private double gpa = 9.5; // only within this class

public void displayAll() {
    // All accessible within the same class
    System.out.println("Name: " + name);
    System.out.println("Roll No: " + rollNo);
    System.out.println("Grade: " + grade);
    System.out.println("GPA: " + gpa);
}

} AccessTest.java (in OtherPkg — different package) javapackage OtherPkg;

import StudentPkg.Student;

public class AccessTest { public static void main(String[] args) { Student s = new Student();

    // ✅ public — accessible
    System.out.println("Name: " + s.name);

    // ❌ protected — NOT accessible from different non-subclass package
    // System.out.println(s.rollNo);  // Compile error

    // ❌ default — NOT accessible from different package
    // System.out.println(s.grade);   // Compile error

    // ❌ private — never accessible outside class
    // System.out.println(s.gpa);     // Compile error

    System.out.println("Only public members are accessible from OtherPkg!");

    // Call public method (which internally accesses all)
    s.displayAll();
}

}

✅ Question 5 — UtilityPkg: StringUtility with Import Types

💻 Code StringUtility.java (in UtilityPkg) javapackage UtilityPkg;

public class StringUtility {

public String reverse(String str) {
    StringBuilder sb = new StringBuilder(str);
    return sb.reverse().toString();
}

public String toUpperCase(String str) {
    return str.toUpperCase();
}

} MainExplicit.java — uses explicit import javapackage MainPkg;

import UtilityPkg.StringUtility; // explicit import

public class MainExplicit { public static void main(String[] args) { StringUtility su = new StringUtility();

    String word = "hello world";
    System.out.println("Original: " + word);
    System.out.println("Reversed: " + su.reverse(word));
    System.out.println("Uppercase: " + su.toUpperCase(word));
}

} MainWildcard.java — uses wildcard import javapackage MainPkg2;

import UtilityPkg.*; // wildcard import

public class MainWildcard { public static void main(String[] args) { StringUtility su = new StringUtility();

    String word = "Java Programming";
    System.out.println("Original: " + word);
    System.out.println("Reversed: " + su.reverse(word));
    System.out.println("Uppercase: " + su.toUpperCase(word));
}

}

✅ Question 6 — StudentDataPkg: Accept & Calculate Marks

💻 Code Student.java (in StudentDataPkg) javapackage StudentDataPkg; import java.util.Scanner;

public class Student { String name; int rollNo; double marks1, marks2, marks3; double total, average;

public void acceptDetails() {
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter Name: ");
    name = sc.nextLine();
    System.out.print("Enter Roll Number: ");
    rollNo = sc.nextInt();
    System.out.print("Enter Marks of Subject 1: ");
    marks1 = sc.nextDouble();
    System.out.print("Enter Marks of Subject 2: ");
    marks2 = sc.nextDouble();
    System.out.print("Enter Marks of Subject 3: ");
    marks3 = sc.nextDouble();
    total = marks1 + marks2 + marks3;
    average = total / 3;
}

public void displayDetails() {
    System.out.println("\n===== Student Details =====");
    System.out.println("Name       : " + name);
    System.out.println("Roll No    : " + rollNo);
    System.out.println("Marks      : " + marks1 + ", " + marks2 + ", " + marks3);
    System.out.printf("Total      : %.2f%n", total);
    System.out.printf("Average    : %.2f%n", average);
}

} Main.java javapackage StudentDataPkg;

public class Main { public static void main(String[] args) { Student s = new Student(); s.acceptDetails(); s.displayDetails(); } }

✅ Question 7 — ExceptionPkg: try-catch-finally

💻 Code Division.java (in ExceptionPkg) javapackage ExceptionPkg;

public class Division { public double divide(int a, int b) { return a / b; // throws ArithmeticException if b == 0 } } Main.java javapackage ExceptionPkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); Division d = new Division();

    System.out.print("Enter numerator: ");
    int a = sc.nextInt();
    System.out.print("Enter denominator: ");
    int b = sc.nextInt();

    try {
        double result = d.divide(a, b);
        System.out.println("Result: " + result);
    } catch (ArithmeticException e) {
        System.out.println("Exception caught: " + e.getMessage());
        System.out.println("Cannot divide by zero!");
    } finally {
        System.out.println("Finally block: Division operation attempted.");
    }

    sc.close();
}

}

✅ Question 8 — AgePkg: throw and throws

💻 Code AgeValidator.java (in AgePkg) javapackage AgePkg;

public class AgeValidator {

// 'throws' tells callers: this method might throw an exception
public void checkAge(int age) throws Exception {
    if (age < 18) {
        // 'throw' actually creates and throws the exception
        throw new Exception("Age " + age + " is below 18. Access denied!");
    }
    System.out.println("Age " + age + " is valid. Access granted!");
}

} Main.java javapackage AgePkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); AgeValidator av = new AgeValidator();

    System.out.print("Enter your age: ");
    int age = sc.nextInt();

    try {
        av.checkAge(age);
    } catch (Exception e) {
        System.out.println("Exception: " + e.getMessage());
    }

    sc.close();
}

}

✅ Question 9 — EmployeePkg: Custom Exception

💻 Code InvalidSalaryException.java (in EmployeePkg) javapackage EmployeePkg;

// Custom checked exception public class InvalidSalaryException extends Exception { public InvalidSalaryException(String message) { super(message); // passes message to parent Exception class } } Employee.java javapackage EmployeePkg;

public class Employee { private String name; private double salary; private static final double MIN_SALARY = 15000.0;

public Employee(String name, double salary) throws InvalidSalaryException {
    if (salary < MIN_SALARY) {
        throw new InvalidSalaryException(
            "Salary Rs." + salary + " is below minimum limit of Rs." + MIN_SALARY
        );
    }
    this.name = name;
    this.salary = salary;
}

public void display() {
    System.out.println("Employee: " + name + " | Salary: Rs." + salary);
}

} Main.java javapackage EmployeePkg; import java.util.Scanner;

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

    System.out.print("Enter employee name: ");
    String name = sc.next();
    System.out.print("Enter salary: ");
    double salary = sc.nextDouble();

    try {
        Employee emp = new Employee(name, salary);
        emp.display();
    } catch (InvalidSalaryException e) {
        System.out.println("Custom Exception Caught: " + e.getMessage());
    }

    sc.close();
}

}

✅ Question 10 — ArrayListPkg: Student Manager

💻 Code Student.java (in ArrayListPkg) javapackage ArrayListPkg;

public class Student { int id; String name; double marks;

public Student(int id, String name, double marks) {
    this.id = id;
    this.name = name;
    this.marks = marks;
}

@Override
public String toString() {
    return "ID: " + id + " | Name: " + name + " | Marks: " + marks;
}

} StudentManager.java javapackage ArrayListPkg; import java.util.ArrayList;

public class StudentManager { private ArrayList<?Student> list = new ArrayList<>();

public void addStudent(Student s) {
    list.add(s);
    System.out.println("Student added: " + s.name);
}

public void removeStudent(int id) {
    for (int i = 0; i < list.size(); i++) {
        if (list.get(i).id == id) {
            System.out.println("Removed: " + list.get(i).name);
            list.remove(i);
            return;
        }
    }
    System.out.println("Student with ID " + id + " not found.");
}

public void searchStudent(int id) {
    for (Student s : list) {
        if (s.id == id) {
            System.out.println("Found: " + s);
            return;
        }
    }
    System.out.println("Student with ID " + id + " not found.");
}

public void displayAll() {
    if (list.isEmpty()) {
        System.out.println("No students in list.");
        return;
    }
    System.out.println("===== All Students =====");
    for (Student s : list) {
        System.out.println(s);
    }
}

} Main.java javapackage ArrayListPkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { StudentManager sm = new StudentManager(); Scanner sc = new Scanner(System.in); int choice;

    do {
        System.out.println("\n1-Add  2-Remove  3-Search  4-Display  5-Exit");
        System.out.print("Choice: ");
        choice = sc.nextInt();

        switch (choice) {
            case 1:
                System.out.print("ID: "); int id = sc.nextInt();
                System.out.print("Name: "); String name = sc.next();
                System.out.print("Marks: "); double marks = sc.nextDouble();
                sm.addStudent(new Student(id, name, marks));
                break;
            case 2:
                System.out.print("Enter ID to remove: ");
                sm.removeStudent(sc.nextInt());
                break;
            case 3:
                System.out.print("Enter ID to search: ");
                sm.searchStudent(sc.nextInt());
                break;
            case 4:
                sm.displayAll();
                break;
        }
    } while (choice != 5);

    sc.close();
}

}

✅ Question 11 — ArrayListSortPkg: Sorting with Comparator

💻 Code Employee.java (in ArrayListSortPkg) javapackage ArrayListSortPkg;

public class Employee { int id; String name; double salary;

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

@Override
public String toString() {
    return "ID: " + id + " | " + name + " | Salary: " + salary;
}

} Main.java javapackage ArrayListSortPkg;

import java.util.; import java.util.stream.;

public class Main { public static void main(String[] args) { ArrayList <?Employee> empList = new ArrayList<>(); Scanner sc = new Scanner(System.in);

    System.out.print("How many employees? ");
    int n = sc.nextInt();

    for (int i = 0; i < n; i++) {
        System.out.print("Enter ID, Name, Salary: ");
        int id = sc.nextInt();
        String name = sc.next();
        double salary = sc.nextDouble();
        empList.add(new Employee(id, name, salary));
    }

    // Sort by salary using Comparator (lambda)
    Collections.sort(empList, (a, b) -> Double.compare(a.salary, b.salary));

    System.out.println("\n--- Sorted by Salary (Ascending) ---");
    for (Employee e : empList) {
        System.out.println(e);
    }

    // Filter employees with salary above threshold
    System.out.print("\nEnter salary threshold to filter: ");
    double threshold = sc.nextDouble();

    List<Employee> filtered = empList.stream()
        .filter(e -> e.salary > threshold)
        .collect(Collectors.toList());

    System.out.println("--- Employees with salary above " + threshold + " ---");
    if (filtered.isEmpty()) System.out.println("None found.");
    else filtered.forEach(System.out::println);

    sc.close();
}

}

✅ Question 12 — LinkedListPkg: Task Manager

💻 Code Task.java (in LinkedListPkg) javapackage LinkedListPkg;

public class Task { int taskId; String taskName;

public Task(int taskId, String taskName) {
    this.taskId = taskId;
    this.taskName = taskName;
}

@Override
public String toString() {
    return "Task[" + taskId + "]: " + taskName;
}

} TaskManager.java javapackage LinkedListPkg; import java.util.LinkedList;

public class TaskManager { private LinkedList<?Task> taskList = new LinkedList<>();

public void addAtBeginning(Task t) {
    taskList.addFirst(t);
    System.out.println("Added at beginning: " + t);
}

public void addAtEnd(Task t) {
    taskList.addLast(t);
    System.out.println("Added at end: " + t);
}

public void removeTask(int taskId) {
    boolean found = taskList.removeIf(t -> t.taskId == taskId);
    System.out.println(found ? "Task " + taskId + " removed."
                             : "Task " + taskId + " not found.");
}

public void displayTasks() {
    if (taskList.isEmpty()) {
        System.out.println("No tasks.");
        return;
    }
    System.out.println("--- Task List ---");
    for (Task t : taskList) System.out.println(t);
}

} Main.java javapackage LinkedListPkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { TaskManager tm = new TaskManager(); Scanner sc = new Scanner(System.in); int choice;

    do {
        System.out.println("\n1-Add Beginning  2-Add End  3-Remove  4-Display  5-Exit");
        System.out.print("Choice: ");
        choice = sc.nextInt();

        switch (choice) {
            case 1:
            case 2:
                System.out.print("Task ID: "); int id = sc.nextInt();
                System.out.print("Task Name: "); String name = sc.next();
                Task t = new Task(id, name);
                if (choice == 1) tm.addAtBeginning(t);
                else tm.addAtEnd(t);
                break;
            case 3:
                System.out.print("Enter Task ID to remove: ");
                tm.removeTask(sc.nextInt());
                break;
            case 4:
                tm.displayTasks();
                break;
        }
    } while (choice != 5);
    sc.close();
}

}

✅ Question 13 — QueuePkg: Queue Simulation

💻 Code QueueDemo.java (in QueuePkg) javapackage QueuePkg; import java.util.LinkedList; import java.util.Queue;

public class QueueDemo { private Queue<?Integer> queue = new LinkedList<>();

public void enqueue(int value) {
    queue.offer(value);
    System.out.println(value + " enqueued.");
}

public void dequeue() throws Exception {
    if (queue.isEmpty()) {
        throw new Exception("Queue Underflow! Queue is empty.");
    }
    System.out.println(queue.poll() + " dequeued.");
}

public void peek() throws Exception {
    if (queue.isEmpty()) {
        throw new Exception("Queue is empty! Nothing to peek.");
    }
    System.out.println("Front element: " + queue.peek());
}

public void display() {
    System.out.println("Queue: " + queue);
}

} Main.java javapackage QueuePkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { QueueDemo q = new QueueDemo(); Scanner sc = new Scanner(System.in); int choice;

    do {
        System.out.println("\n1-Enqueue  2-Dequeue  3-Peek  4-Display  5-Exit");
        System.out.print("Choice: ");
        choice = sc.nextInt();

        try {
            switch (choice) {
                case 1:
                    System.out.print("Enter value: ");
                    q.enqueue(sc.nextInt());
                    break;
                case 2: q.dequeue(); break;
                case 3: q.peek(); break;
                case 4: q.display(); break;
            }
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    } while (choice != 5);

    sc.close();
}

}

✅ Question 14 — VectorPkg: Thread-Safe Vector

💻 Code Product.java (in VectorPkg) javapackage VectorPkg;

public class Product { int id; String name; double price;

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

@Override
public String toString() {
    return "Product[" + id + "]: " + name + " @ Rs." + price;
}

} Main.java javapackage VectorPkg; import java.util.Vector; import java.util.Scanner;

public class Main { public static void main(String[] args) { Vector<?Product> products = new Vector<>(); Scanner sc = new Scanner(System.in);

    System.out.print("How many products to add? ");
    int n = sc.nextInt();

    for (int i = 0; i < n; i++) {
        System.out.print("Enter ID, Name, Price: ");
        int id = sc.nextInt();
        String name = sc.next();
        double price = sc.nextDouble();
        products.add(new Product(id, name, price));
    }

    System.out.println("\n--- All Products ---");
    for (Product p : products) System.out.println(p);

    System.out.print("\nEnter index to remove (0-based): ");
    int idx = sc.nextInt();
    if (idx >= 0 && idx < products.size()) {
        System.out.println("Removed: " + products.remove(idx));
    } else {
        System.out.println("Invalid index.");
    }

    System.out.println("\n--- After Removal ---");
    products.forEach(System.out::println);

    // Demonstrate thread-safe behavior
    System.out.println("\nVector size: " + products.size());
    System.out.println("Vector is synchronized (thread-safe).");

    sc.close();
}

}

✅ Question 15 — StackPkg: Postfix Expression Evaluator

💻 Code StackDemo.java (in StackPkg) javapackage StackPkg; import java.util.Stack;

public class StackDemo { private Stack<?Double> stack = new Stack<>();

public double evaluatePostfix(String expression) throws Exception {
    String[] tokens = expression.trim().split("\\s+");

    for (String token : tokens) {
        if (isNumber(token)) {
            stack.push(Double.parseDouble(token));
        } else if (isOperator(token)) {
            if (stack.size() < 2) {
                throw new Exception("Invalid expression: not enough operands.");
            }
            double b = stack.pop();
            double a = stack.pop();
            double result = applyOperator(token, a, b);
            stack.push(result);
            System.out.println("  " + a + " " + token + " " + b + " = " + result);
        } else {
            throw new Exception("Unknown token: " + token);
        }
    }

    if (stack.size() != 1) {
        throw new Exception("Invalid expression.");
    }
    return stack.pop();
}

private boolean isNumber(String s) {
    try { Double.parseDouble(s); return true; }
    catch (NumberFormatException e) { return false; }
}

private boolean isOperator(String s) {
    return s.equals("+") || s.equals("-") ||
           s.equals("*") || s.equals("/");
}

private double applyOperator(String op, double a, double b) throws Exception {
    switch (op) {
        case "+": return a + b;
        case "-": return a - b;
        case "*": return a * b;
        case "/":
            if (b == 0) throw new Exception("Division by zero!");
            return a / b;
        default: throw new Exception("Unknown operator: " + op);
    }
}

// Stack operations
public void push(double val) { stack.push(val); System.out.println("Pushed: " + val); }

public double pop() throws Exception {
    if (stack.isEmpty()) throw new Exception("Stack Underflow!");
    double val = stack.pop(); System.out.println("Popped: " + val); return val;
}

public double peek() throws Exception {
    if (stack.isEmpty()) throw new Exception("Stack is empty!");
    return stack.peek();
}

} Main.java javapackage StackPkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); StackDemo sd = new StackDemo();

    System.out.println("Enter postfix expression (e.g., 3 4 + 2 *):");
    sc.nextLine();
    String expr = sc.nextLine();

    try {
        double result = sd.evaluatePostfix(expr);
        System.out.println("Result: " + result);
    } catch (Exception e) {
        System.out.println("Error: " + e.getMessage());
    }

    sc.close();
}

}

✅ Question 16 — HashSetPkg: Unique Courses

💻 Code Course.java (in HashSetPkg) javapackage HashSetPkg; import java.util.Objects;

public class Course { int courseId; String courseName;

public Course(int courseId, String courseName) {
    this.courseId = courseId;
    this.courseName = courseName;
}

@Override
public boolean equals(Object obj) {
    if (this == obj) return true;
    if (!(obj instanceof Course)) return false;
    Course c = (Course) obj;
    return this.courseId == c.courseId &&
           this.courseName.equals(c.courseName);
}

@Override
public int hashCode() {
    return Objects.hash(courseId, courseName);
}

@Override
public String toString() {
    return "Course[" + courseId + "]: " + courseName;
}

} Main.java javapackage HashSetPkg; import java.util.HashSet;

public class Main { public static void main(String[] args) { HashSet<?Course> courseSet = new HashSet<>();

    courseSet.add(new Course(101, "Java Programming"));
    courseSet.add(new Course(102, "Data Structures"));
    courseSet.add(new Course(101, "Java Programming")); // duplicate — will be ignored
    courseSet.add(new Course(103, "Web Development"));

    System.out.println("Unique Courses (size=" + courseSet.size() + "):");
    for (Course c : courseSet) {
        System.out.println(c);
    }
}

}

✅ Question 17 — LinkedHashSetPkg: Insertion-Order Books

💻 Code Book.java (in LinkedHashSetPkg) javapackage LinkedHashSetPkg; import java.util.Objects;

public class Book { int bookId; String bookName;

public Book(int bookId, String bookName) {
    this.bookId = bookId;
    this.bookName = bookName;
}

@Override
public boolean equals(Object o) {
    if (!(o instanceof Book)) return false;
    Book b = (Book) o;
    return bookId == b.bookId && bookName.equals(b.bookName);
}

@Override
public int hashCode() {
    return Objects.hash(bookId, bookName);
}

@Override
public String toString() {
    return "Book[" + bookId + "]: " + bookName;
}

} Main.java javapackage LinkedHashSetPkg; import java.util.LinkedHashSet;

public class Main { public static void main(String[] args) { LinkedHashSet<?Book> bookSet = new LinkedHashSet<>();

    bookSet.add(new Book(1, "Clean Code"));
    bookSet.add(new Book(2, "Effective Java"));
    bookSet.add(new Book(3, "Design Patterns"));
    bookSet.add(new Book(1, "Clean Code"));   // duplicate — ignored
    bookSet.add(new Book(4, "The Pragmatic Programmer"));

    System.out.println("Books (insertion order maintained, size=" + bookSet.size() + "):");
    for (Book b : bookSet) {
        System.out.println(b);
    }
}

}

✅ Question 18 — TreeSetPkg: Sorted Players using Comparable

💻 Code Player.java (in TreeSetPkg) javapackage TreeSetPkg;

public class Player implements Comparable<?Player> { int id; int score;

public Player(int id, int score) {
    this.id = id;
    this.score = score;
}

@Override
public int compareTo(Player other) {
    // Sort by score ascending; if equal, sort by id
    if (this.score != other.score)
        return Integer.compare(this.score, other.score);
    return Integer.compare(this.id, other.id);
}

@Override
public String toString() {
    return "Player[ID=" + id + ", Score=" + score + "]";
}

} Main.java javapackage TreeSetPkg; import java.util.TreeSet; import java.util.Scanner;

public class Main { public static void main(String[] args) { TreeSet<?Player> playerSet = new TreeSet<>(); Scanner sc = new Scanner(System.in);

    System.out.print("How many players? ");
    int n = sc.nextInt();

    for (int i = 0; i < n; i++) {
        System.out.print("Enter player ID and Score: ");
        int id = sc.nextInt();
        int score = sc.nextInt();
        playerSet.add(new Player(id, score));
    }

    System.out.println("\n--- Players sorted by Score ---");
    for (Player p : playerSet) {
        System.out.println(p);
    }

    sc.close();
}

}

✅ Question 19 — TreeMapPkg: Library with TreeMap

💻 Code Library.java (in TreeMapPkg) javapackage TreeMapPkg; import java.util.TreeMap; import java.util.Map;

public class Library { private TreeMap<?Integer, String> books = new TreeMap<>();

public void addBook(int id, String name) {
    books.put(id, name);
    System.out.println("Added: [" + id + "] " + name);
}

public void removeBook(int id) {
    if (books.containsKey(id)) {
        System.out.println("Removed: [" + id + "] " + books.remove(id));
    } else {
        System.out.println("Book ID " + id + " not found.");
    }
}

public void searchBook(int id) {
    String name = books.get(id);
    if (name != null) System.out.println("Found: [" + id + "] " + name);
    else System.out.println("Book ID " + id + " not found.");
}

public void displayAll() {
    if (books.isEmpty()) { System.out.println("Library is empty."); return; }
    System.out.println("--- Library (sorted by Book ID) ---");
    for (Map.Entry<Integer, String> entry : books.entrySet()) {
        System.out.println("[" + entry.getKey() + "] " + entry.getValue());
    }
}

} Main.java javapackage TreeMapPkg; import java.util.Scanner;

public class Main { public static void main(String[] args) { Library lib = new Library(); Scanner sc = new Scanner(System.in); int choice;

    do {
        System.out.println("\n1-Add  2-Remove  3-Search  4-Display  5-Exit");
        System.out.print("Choice: ");
        choice = sc.nextInt();

        switch (choice) {
            case 1:
                System.out.print("Book ID: "); int id = sc.nextInt();
                System.out.print("Book Name: "); String name = sc.next();
                lib.addBook(id, name);
                break;
            case 2:
                System.out.print("Book ID to remove: ");
                lib.removeBook(sc.nextInt());
                break;
            case 3:
                System.out.print("Book ID to search: ");
                lib.searchBook(sc.nextInt());
                break;
            case 4:
                lib.displayAll();
                break;
        }
    } while (choice != 5);

    sc.close();
}

}

1 Create a base class Animal with a method eat() and extend it with a subclass Dog that includes an additional method bark(). Demonstrate how inheritance allows the Dog class to access both its own method and the inherited method. CODE: class Animal { void eat(){ System.out.println("This animal eats foods."); } } class Dog extends Animal{ void bark(){ System.err.println("The dog barks."); } public static void main(String[] args) { Dog obj= new Dog();
obj.eat();
obj.bark(); } }

2 Design three classes A, B, and C such that class B inherits from A and class C inherits from B. Show how multilevel inheritance enables class C to access properties and methods of both A and B. CODE: class A {
void showA(){ System.out.println("This is class A."); } } class B extends A{
void showB(){ System.out.println("This class B will inherit from A.");

} 

} class C extends B{
void showC(){ System.out.println("This class C will inherit from B & A both."); }

public static void main(String[]args){
C obj = new C();
obj.showA();
obj.showB();
obj.showC(); } }

3 Create a parent class Parent and derive two child classes Child1 and Child2 from it. Illustrate how hierarchical inheritance allows both child classes to share common features of the parent class. CODE:

class Parent{
void showParent(){ System.out.println("This is the Parent class."); } }

class Son extends Parent{
void showSon(){ System.out.println("This is the first child."); } } class Daughter extends Parent{
void showDaughter(){ System.out.println("This is the second child."); } public static void main(String[]args){
Son obj1=new Son();
obj1.showParent();
obj1.showSon(); Daughter obj2= new Daughter();
obj2.showParent();
obj2.showDaughter(); } }

4 Create a class that contains multiple methods named add() with different parameter lists. Demonstrate how method overloading achieves compile-time polymorphism by selecting the appropriate method based on arguments. CODE:
class Mathematics{
int add(int a, int b){ return a+b; } double add(double a,double b){ return a+b; } int add(int a, int b, int c){ return a+b+c; } public static void main(String[] args){ Mathematics obj = new Mathematics(); System.out.println(obj.add(12,22)); System.out.println(obj.add(33.9,9.0)); System.out.println(obj.add(44,3,22)); } }

5 Define a method in a parent class and override the same method in a child class. Demonstrate runtime polymorphism by calling the overridden method using a parent class reference. CODE: class Animal { void sound() { System.out.println("Animal makes a sound."); } } class Dogs extends Animal { @Override void sound() { System.out.println("Dog is barking."); }

public static void main(String[] args) {
    Animal obj = new Dogs(); 
    obj.sound(); 
} 

}

6 Create an abstract class Shape with an abstract method draw(). Implement this method in a subclass and demonstrate how abstraction hides implementation details. CODE: abstract class Shape{ abstract void draw(); } class Circle extends Shape{ void draw(){ System.out.println("Draw a circle"); } public static void main(String[]args){ Shape obj = new Circle(); obj.draw(); } }

7 Create a class with private data members and provide public getter and setter methods to access them. Demonstrate how encapsulation ensures data hiding and controlled access. CODE: class Student{ private int age; private String name;

public int getAge(){ 
    return age; 

} 
public void setAge(int age){ 
    this.age=age; 
} 
public String getName(){ 
    return name; 
} 
public void setName(String name){ 
    this.name=name; 
} 
public static void main(String[]args){ 
    Student obj =new Student(); 
    obj.setAge(21); 
    obj.setName("Anuja"); 

 
System.out.println("Age:"+  obj.getAge()); 
System.out.println("Name:"+ obj.getName()); 

}}

8 Create a class that includes both a default constructor and a parameterized constructor. Show how constructors are used to initialize objects in different ways. CODE: class Students{ int age; String name; Students(){ age=18; name="Default"; } Students(int a,String n){ age = a; name=n; } void display(){ System.out.println("Age: "+age + ", Name: "+ name);

} 
public static void main(String[]args){ 
    Students s1 = new Students(); 
    s1.display(); 

    Students s2 = new Students(21,"Anuja"); 
    s2.display(); 
} 

}

9 Create a class with multiple constructors and use this() to call one constructor from another. Demonstrate how constructor chaining helps in code reusability and proper initialization. CODE: class Studentss {int age; String name; Studentss() { this(18, "Default");
System.out.println("Default constructor called"); } Studentss(int age, String name) { this.age = age; this.name = name; System.out.println("Parameterized constructor called"); } void display() { System.out.println("Age: " + age + ", Name: " + name); } public static void main(String[] args) { Studentss s1 = new Studentss(); s1.display(); } }

10.Create a class that demonstrates the use of final, static, and abstract keywords. Illustrate how these modifiers affect variables, methods, and class behavior in Java. CODE: abstract class Shapes {

static String type = "Shapes"; 

final int sides = 0; 

abstract void draw(); 

final void showType() { 
    System.out.println("This is a " + type); 
 } 

static void info() { 
    System.out.println("Static method in abstract class"); 
} 

}

class Circle extends Shapes {

void draw() { 
    System.out.println("Draw a circle"); 
} 
public static void main(String[] args) { 

Shapes.info();    

Circle obj = new Circle(); 

obj.draw();       
obj.showType();   

System.out.println("Sides: " + obj.sides); 

} }