Question:

You are given the following class hierarchy:

public class Animal {
    // attributes and methods
}

public class Mammal extends Animal {
    // attributes and methods
}

public class Elephant extends Mammal {
    // attributes and methods
}

public class ThrowExceptionExample {
    public static void checkAnimal(Animal animal) {
        // code to check if the animal is a Mammal
        // if it is not a Mammal, throw a new IllegalArgumentException with a message "Animal must be a Mammal!"
    }
    
    public static void main(String[] args) {
        Animal animal1 = new Elephant();
        Animal animal2 = new Animal();
        
        // Call checkAnimal method for animal1
        // Call checkAnimal method for animal2
    }
}

Your task is to complete the checkAnimal method in the ThrowExceptionExample class. The method should throw a new IllegalArgumentException if the animal parameter is not an instance of the Mammal class. The exception message should be "Animal must be a Mammal!".

In the main method, two animal objects are created: animal1, which is an instance of the Elephant class, and animal2, which is an instance of the Animal class. You need to call the checkAnimal method for both animal1 and animal2 and handle any exceptions that may be thrown.

Write the code for the checkAnimal method and handle any exceptions in the main method. Provide step-by-step detailed explanation of the code.

Answer:

public static void checkAnimal(Animal animal) {
    if (!(animal instanceof Mammal)) {
        throw new IllegalArgumentException("Animal must be a Mammal!");
    }
}
    
public static void main(String[] args) {
    Animal animal1 = new Elephant();
    Animal animal2 = new Animal();
        
    try {
        checkAnimal(animal1);
        System.out.println("animal1 is a Mammal.");
    } catch (IllegalArgumentException e) {
        System.out.println(e.getMessage());
    }
        
    try {
        checkAnimal(animal2);
        System.out.println("animal2 is a Mammal.");
    } catch (IllegalArgumentException e) {
        System.out.println(e.getMessage());
    }
}

Explanation:

1. The checkAnimal method takes an Animal object as a parameter.
2. The if statement checks if the animal parameter is not an instance of the Mammal class using the instanceof operator.
3. If the animal is not a Mammal, an IllegalArgumentException is thrown with the message "Animal must be a Mammal!".
4. In the main method, a try-catch block is used to handle any exceptions that may be thrown by the checkAnimal method.
5. animal1 is an instance of the Elephant class, which is a subclass of Mammal. So, calling the checkAnimal method for animal1 will not throw an exception.
6. The statement System.out.println("animal1 is a Mammal."); is executed, indicating that animal1 is indeed a mammal.
7. animal2 is an instance of the Animal class, which is not a subclass of Mammal. So, calling the checkAnimal method for animal2 will throw an exception.
8. The catch block catches the thrown IllegalArgumentException and executes the statement System.out.println(e.getMessage());, which will print the exception message "Animal must be a Mammal!".