Upcasting and downcasting in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Upcasting and Method Calls

What is the output of this Java code snippet?

Java

class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}
class Dog extends Animal {
    void sound() {
        System.out.println("Dog barks");
    }
    void fetch() {
        System.out.println("Dog fetches ball");
    }
}
public class Test {
    public static void main(String[] args) {
        Animal a = new Dog(); // upcasting
        a.sound();
    }
}

A Animal sound

B Dog fetches ball

C Dog barks

D Compilation error

💡 Hint

Remember that overridden methods use the actual object's method, even if referenced by a parent type.

The variable 'a' is of type Animal but refers to a Dog object. The sound() method is overridden in Dog, so Dog's version runs.

❓ Predict Output

intermediate

Downcasting and Method Access

What will be the output of this Java code?

Java

class Vehicle {
    void start() {
        System.out.println("Vehicle started");
    }
}
class Car extends Vehicle {
    void openSunroof() {
        System.out.println("Sunroof opened");
    }
}
public class Test {
    public static void main(String[] args) {
        Vehicle v = new Car(); // upcasting
        ((Car) v).openSunroof(); // downcasting
    }
}

A Sunroof opened

B Vehicle started

C ClassCastException at runtime

D Compilation error

💡 Hint

Downcasting allows access to subclass-specific methods.

The object 'v' is actually a Car, so downcasting to Car is safe and allows calling openSunroof().

❓ Predict Output

advanced

Runtime Error from Invalid Downcasting

What error does this code produce when run?

Java

class Fruit {
    void eat() {
        System.out.println("Eating fruit");
    }
}
class Apple extends Fruit {
    void peel() {
        System.out.println("Peeling apple");
    }
}
class Orange extends Fruit {
    void peel() {
        System.out.println("Peeling orange");
    }
}
public class Test {
    public static void main(String[] args) {
        Fruit f = new Orange();
        Apple a = (Apple) f; // downcasting
        a.peel();
    }
}

A ClassCastException at runtime

B Peeling orange

C Peeling apple

D Compilation error

💡 Hint

Downcasting to a wrong subclass causes runtime errors.

The object is an Orange but cast to Apple, causing ClassCastException at runtime.

🧠 Conceptual

advanced

Understanding Upcasting Behavior

Given the code below, what will be the output when main runs?

Java

class Parent {
    void show() {
        System.out.println("Parent show");
    }
}
class Child extends Parent {
    void show() {
        System.out.println("Child show");
    }
    void play() {
        System.out.println("Child play");
    }
}
public class Test {
    public static void main(String[] args) {
        Parent p = new Child(); // upcasting
        p.show();
        // p.play(); // commented out
    }
}

A Parent show

B Child show

C Child play

D Compilation error due to p.play()

💡 Hint

Upcasting hides subclass-only methods but overridden methods run subclass versions.

The show() method is overridden, so Child's version runs. The play() method is not accessible via Parent reference.

❓ Predict Output

expert

Output and Behavior of Complex Casting

What is the output of this Java program?

Java

class A {
    void m() {
        System.out.println("A.m()");
    }
}
class B extends A {
    void m() {
        System.out.println("B.m()");
    }
    void n() {
        System.out.println("B.n()");
    }
}
class C extends B {
    void m() {
        System.out.println("C.m()");
    }
    void n() {
        System.out.println("C.n()");
    }
}
public class Test {
    public static void main(String[] args) {
        A obj = new C(); // upcasting
        obj.m();
        ((B) obj).n(); // downcasting
    }
}

A Compilation error

B C.m()\nB.n()

C A.m()\nB.n()

D C.m()\nC.n()

💡 Hint

Method calls use the actual object's version, even after casting.

obj refers to a C object. m() is overridden in C, so C.m() runs. Downcasting to B allows calling n(), but n() is overridden in C, so C.n() runs.