Write a program to define user defined exceptions and raise them as per the requirements.

Code:

class InvalidAgeException extends Exception {
    public InvalidAgeException(String message) {
        super(message);
    }
}

class User {
    private String name;
    private int age;

    public User(String name, int age) throws InvalidAgeException {
        if (age < 18) {
            throw new InvalidAgeException("Age must be 18 or older.");
        }
        this.name = name;
        this.age = age;
    }

    public void displayUserInfo() {
        System.out.println("Name: " + name);
        System.out.println("Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        try {
            User user1 = new User("John", 25);
            user1.displayUserInfo();

            User user2 = new User("Alice", 16); // This will throw an exception
            user2.displayUserInfo(); // This won't be executed due to the exception
        } catch (InvalidAgeException e) {
            System.out.println("InvalidAgeException caught: " + e.getMessage());
        }
    }
}




Write a program to implement the concepts of Abstract classes and 
methods.

// Abstract class
abstract class Shape {
    // Abstract method
    abstract double calculateArea();
    
    // Concrete method
    void display() {
        System.out.println("This is a shape.");
    }
}

// Concrete subclass Circle
class Circle extends Shape {
    double radius;
    
    Circle(double radius) {
        this.radius = radius;
    }
    
    // Implementation of abstract method
    @Override
    double calculateArea() {
        return Math.PI * radius * radius;
    }
}

// Concrete subclass Rectangle
class Rectangle extends Shape {
    double length;
    double width;
    
    Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }
    
    // Implementation of abstract method
    @Override
    double calculateArea() {
        return length * width;
    }
}

public class Main {
    public static void main(String[] args) {
        // Creating objects of concrete subclasses
        Circle circle = new Circle(5);
        Rectangle rectangle = new Rectangle(4, 6);
        
        // Calling methods on objects
        circle.display();
        System.out.println("Area of circle: " + circle.calculateArea());
        
        rectangle.display();
        System.out.println("Area of rectangle: " + rectangle.calculateArea());
    }
}




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