Upcasting and downcasting in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to upcast a Dog object to an Animal reference.

Java

Animal animal = new Dog(); // [1]

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Aoverriding

Bdowncasting

Cupcasting

Doverloading

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing upcasting with downcasting.

Trying to cast explicitly when not needed.

Upcasting means treating a subclass object as an instance of its superclass. Here, Dog is upcast to Animal.

2fill in blank

medium

Complete the code to downcast an Animal reference back to a Dog object.

Java

Dog dog = (Dog) [1];

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Aanimal

Bnew Animal()

Cnew Dog()

Danimal.toString()

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to cast a new Animal object instead of the reference.

Missing the explicit cast.

Downcasting requires an explicit cast. Here, the Animal reference named 'animal' is cast back to Dog.

3fill in blank

hard

Fix the error in the downcasting code to avoid ClassCastException.

Java

if ([1] instanceof Dog) {
    Dog dog = (Dog) animal;
}

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Adog

Banimal

Cnew Animal()

Dnew Dog()

Attempts:

3 left

💡 Hint

Common Mistakes

Checking instanceof on the wrong variable.

Not using instanceof before downcasting.

Before downcasting, check if the object referenced by 'animal' is an instance of Dog to avoid errors.

4fill in blank

hard

Fill both blanks to create a list of Animals and add a Dog object using upcasting.

Java

List<[1]> animals = new ArrayList<>();
animals.add(new [2]());

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AAnimal

BDog

CCat

DObject

Attempts:

3 left

💡 Hint

Common Mistakes

Using Dog as the list type instead of Animal.

Adding an unrelated class object.

The list holds Animal references. Adding a Dog object is upcasting it to Animal.

5fill in blank

hard

Fill all three blanks to safely downcast and call a Dog-specific method.

Java

if ([1] instanceof [2]) {
    [2] dog = ([2]) [3];
    dog.bark();
}

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Aanimal

BDog

CCat

Dobject

Attempts:

3 left

💡 Hint

Common Mistakes

Using the wrong variable for instanceof or casting.

Casting to the wrong class.

Check if 'animal' is a Dog, then downcast it to Dog and call the Dog-specific method bark().