Practice Questions — Inheritance in Java

class Shape {
    double area() { return 0; }
}

class Circle extends Shape {
    double radius;
    Circle(double radius) { this.radius = radius; }
    @Override
    double area() { return Math.PI * radius * radius; }
}

class Rectangle extends Shape {
    double width, height;
    Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    @Override
    double area() { return width * height; }
}

public class Main {
    public static void main(String[] args) {
        Shape c = new Circle(5);
        Shape r = new Rectangle(4, 6);
        System.out.printf("Circle area: %.2f%n", c.area());
        System.out.printf("Rectangle area: %.2f%n", r.area());
    }
}

class Animal {
    String name;
    Animal(String name) { this.name = name; }
    void makeSound() { System.out.println(name + " says: ..."); }
}

class Dog extends Animal {
    Dog() { super("Dog"); }
    @Override
    void makeSound() { System.out.println(name + " says: Woof!"); }
}

class Cat extends Animal {
    Cat() { super("Cat"); }
    @Override
    void makeSound() { System.out.println(name + " says: Meow!"); }
}

class Cow extends Animal {
    Cow() { super("Cow"); }
    @Override
    void makeSound() { System.out.println(name + " says: Moo!"); }
}

public class Main {
    public static void main(String[] args) {
        Animal[] animals = { new Dog(), new Cat(), new Cow() };
        for (Animal a : animals) {
            a.makeSound();
        }
    }
}

class Employee {
    String name;
    double baseSalary;
    Employee(String name, double baseSalary) {
        this.name = name;
        this.baseSalary = baseSalary;
    }
    double calculatePay() { return baseSalary; }
}

class Manager extends Employee {
    double bonus;
    Manager(String name, double baseSalary, double bonus) {
        super(name, baseSalary);
        this.bonus = bonus;
    }
    @Override
    double calculatePay() { return super.calculatePay() + bonus; }
}

class Developer extends Employee {
    int overtimeHours;
    Developer(String name, double baseSalary, int overtimeHours) {
        super(name, baseSalary);
        this.overtimeHours = overtimeHours;
    }
    @Override
    double calculatePay() { return super.calculatePay() + overtimeHours * 500; }
}

public class Main {
    public static void main(String[] args) {
        Employee[] team = {
            new Manager("Kavitha", 80000, 15000),
            new Developer("Rohan", 60000, 20),
            new Developer("Deepak", 55000, 15)
        };
        for (Employee e : team) {
            System.out.println(e.name + " (" + e.getClass().getSimpleName() + "): Rs." + e.calculatePay());
        }
    }
}

class BankAccount {
    String holder;
    double balance;
    BankAccount(String holder, double balance) {
        this.holder = holder;
        this.balance = balance;
    }
    void withdraw(double amount) {
        if (amount > balance) {
            System.out.println("Insufficient funds");
        } else {
            balance -= amount;
            System.out.println("Withdrew Rs." + amount);
        }
    }
    public String toString() {
        return holder + ": Rs." + balance;
    }
}

class SavingsAccount extends BankAccount {
    double interestRate;
    SavingsAccount(String holder, double balance, double rate) {
        super(holder, balance);
        this.interestRate = rate;
    }
    void addInterest() {
        balance += balance * interestRate;
        System.out.println("After interest: Rs." + balance);
    }
}

class CurrentAccount extends BankAccount {
    double overdraftLimit;
    CurrentAccount(String holder, double balance, double limit) {
        super(holder, balance);
        this.overdraftLimit = limit;
    }
    @Override
    void withdraw(double amount) {
        if (amount > balance + overdraftLimit) {
            System.out.println("Exceeds overdraft limit");
        } else {
            balance -= amount;
            System.out.println("Withdrew Rs." + amount + (balance < 0 ? " (using overdraft)" : ""));
        }
    }
}

public class Main {
    public static void main(String[] args) {
        SavingsAccount sa = new SavingsAccount("Priya", 10000, 0.05);
        System.out.println("Savings - " + sa);
        sa.addInterest();

        CurrentAccount ca = new CurrentAccount("Aarav", 5000, 10000);
        System.out.println("Current - " + ca);
        ca.withdraw(7000);
        System.out.println("Balance: Rs." + ca.balance);
    }
}

class Vehicle {
    String brand;
    int year;
    Vehicle(String brand, int year) {
        this.brand = brand;
        this.year = year;
    }
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        Vehicle v = (Vehicle) obj;
        return year == v.year && brand.equals(v.brand);
    }
    @Override
    public int hashCode() { return 31 * brand.hashCode() + year; }
    @Override
    public String toString() { return "Vehicle{" + brand + ", " + year + "}"; }
}

class Car extends Vehicle {
    int numDoors;
    Car(String brand, int year, int numDoors) {
        super(brand, year);
        this.numDoors = numDoors;
    }
    @Override
    public boolean equals(Object obj) {
        if (!super.equals(obj)) return false;
        Car c = (Car) obj;
        return numDoors == c.numDoors;
    }
    @Override
    public int hashCode() { return 31 * super.hashCode() + numDoors; }
    @Override
    public String toString() {
        return "Car{brand='" + brand + "', year=" + year + ", doors=" + numDoors + "}";
    }
}

class Motorcycle extends Vehicle {
    boolean hasSidecar;
    Motorcycle(String brand, int year, boolean hasSidecar) {
        super(brand, year);
        this.hasSidecar = hasSidecar;
    }
    @Override
    public String toString() {
        return "Motorcycle{brand='" + brand + "', year=" + year + ", sidecar=" + hasSidecar + "}";
    }
}

public class Main {
    public static void main(String[] args) {
        Car c1 = new Car("Toyota", 2024, 4);
        Car c2 = new Car("Toyota", 2024, 4);
        System.out.println(c1);
        System.out.println(c2);
        System.out.println("Are they equal? " + c1.equals(c2));

        Motorcycle m = new Motorcycle("Honda", 2023, false);
        System.out.println(m);
        System.out.println("Car equals Motorcycle? " + c1.equals(m));
    }
}

class AppException extends Exception {
    AppException(String msg) { super(msg); }
}

class ValidationException extends AppException {
    ValidationException(String msg) { super(msg); }
}

class NotFoundException extends AppException {
    NotFoundException(String msg) { super(msg); }
}

public class Main {
    static void process(int code) throws AppException {
        if (code == 1) throw new ValidationException("Age must be positive: -5");
        if (code == 2) throw new NotFoundException("Student not found: ID 999");
        if (code == 3) throw new AppException("General application error");
    }

    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            try {
                process(i);
            } catch (ValidationException e) {
                System.out.println("ValidationException: " + e.getMessage());
            } catch (NotFoundException e) {
                System.out.println("NotFoundException: " + e.getMessage());
            } catch (AppException e) {
                System.out.println("AppException: " + e.getMessage());
            }
        }
    }
}