Practice Questions — OOP Basics - Classes, Objects, and Constructors

class Student {
    String name;
    int rollNo;
    double marks;

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

    char getGrade() {
        if (marks >= 90) return 'A';
        if (marks >= 80) return 'B';
        if (marks >= 70) return 'C';
        if (marks >= 60) return 'D';
        return 'F';
    }

    public String toString() {
        return "Student{name='" + name + "', rollNo=" + rollNo
               + ", marks=" + marks + ", grade=" + getGrade() + "}";
    }

    public static void main(String[] args) {
        Student s1 = new Student("Aarav", 101, 92.5);
        Student s2 = new Student("Priya", 102, 78.0);
        System.out.println(s1);
        System.out.println(s2);
    }
}

class BankAccount {
    String accountHolder;
    double balance;

    BankAccount(String accountHolder, double balance) {
        this.accountHolder = accountHolder;
        this.balance = balance;
    }

    void deposit(double amount) {
        if (amount > 0) {
            balance += amount;
            System.out.printf("After deposit: Rs.%.2f%n", balance);
        }
    }

    void withdraw(double amount) {
        if (amount > balance) {
            System.out.printf("Insufficient balance for Rs.%.2f%n", amount);
        } else if (amount > 0) {
            balance -= amount;
            System.out.printf("After withdrawal: Rs.%.2f%n", balance);
        }
    }

    public String toString() {
        return String.format("%s: Rs.%.2f", accountHolder, balance);
    }

    public static void main(String[] args) {
        BankAccount acc = new BankAccount("Kavitha", 5000.0);
        System.out.println(acc);
        acc.deposit(2000);
        acc.withdraw(2500);
        acc.withdraw(5000);
    }
}

class Product {
    String name;
    double price;
    static int totalProducts = 0;

    Product(String name, double price) {
        this.name = name;
        this.price = price;
        totalProducts++;
    }

    public String toString() {
        return "Product: " + name + " - Rs." + price + " (Total: " + totalProducts + ")";
    }

    public static void main(String[] args) {
        System.out.println(new Product("Laptop", 50000.0));
        System.out.println(new Product("Phone", 20000.0));
        System.out.println(new Product("Tablet", 15000.0));
        System.out.println("Total products created: " + Product.totalProducts);
    }
}

class Complex {
    double real, imag;

    Complex(double real, double imag) {
        this.real = real;
        this.imag = imag;
    }

    Complex add(Complex other) {
        return new Complex(this.real + other.real, this.imag + other.imag);
    }

    Complex multiply(Complex other) {
        double r = this.real * other.real - this.imag * other.imag;
        double i = this.real * other.imag + this.imag * other.real;
        return new Complex(r, i);
    }

    public String toString() {
        return real + " + " + imag + "i";
    }

    public static void main(String[] args) {
        Complex a = new Complex(2, 3);
        Complex b = new Complex(1, 4);
        Complex c = new Complex(5, 0);
        System.out.println("a = " + a);
        System.out.println("b = " + b);
        System.out.println("c = " + c);
        System.out.println("a + b = " + a.add(b));
        System.out.println("(a + b) * c = " + a.add(b).multiply(c));
    }
}

class Node {
    int data;
    Node next;

    Node(int data) {
        this.data = data;
        this.next = null;
    }

    Node(int data, Node next) {
        this.data = data;
        this.next = next;
    }

    static void printList(Node head) {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " -> ");
            current = current.next;
        }
        System.out.println("null");
    }

    public static void main(String[] args) {
        Node head = new Node(10, new Node(20, new Node(30, new Node(40))));
        printList(head);
    }
}

class Student {
    String name;
    int rollNo;
    double marks;

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

    public String toString() {
        return "Student{name='" + name + "', rollNo=" + rollNo + ", marks=" + marks + "}";
    }
}

class StudentBuilder {
    String name;
    int rollNo;
    double marks;

    StudentBuilder setName(String name) {
        this.name = name;
        return this;
    }

    StudentBuilder setRollNo(int rollNo) {
        this.rollNo = rollNo;
        return this;
    }

    StudentBuilder setMarks(double marks) {
        this.marks = marks;
        return this;
    }

    Student build() {
        return new Student(name, rollNo, marks);
    }

    public static void main(String[] args) {
        Student s = new StudentBuilder()
            .setName("Deepak")
            .setRollNo(201)
            .setMarks(91.5)
            .build();
        System.out.println(s);
    }
}

class Point {
    final int x;
    final int y;

    Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    Point translate(int dx, int dy) {
        return new Point(this.x + dx, this.y + dy);
    }

    double distanceTo(Point other) {
        int dx = this.x - other.x;
        int dy = this.y - other.y;
        return Math.sqrt(dx * dx + dy * dy);
    }

    public String toString() {
        return "(" + x + ", " + y + ")";
    }

    public static void main(String[] args) {
        Point p = new Point(3, 4);
        System.out.println("Original: " + p);

        Point moved = p.translate(2, 3);
        System.out.println("Translated: " + moved);
        System.out.println("Original unchanged: " + p);

        Point origin = new Point(0, 0);
        System.out.printf("Distance to origin: %.2f%n", p.distanceTo(origin));
    }
}