Method overriding rules in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of overridden method with super call

What is the output of this Java program?

Java

class Parent {
    void show() {
        System.out.println("Parent show");
    }
}

class Child extends Parent {
    @Override
    void show() {
        System.out.println("Child show");
        super.show();
    }
}

public class Test {
    public static void main(String[] args) {
        Parent obj = new Child();
        obj.show();
    }
}

A Parent show\nChild show

B Child show\nParent show

C Child show

D Parent show

💡 Hint

Remember that the overridden method in the child class calls super.show() after printing.

The object is of type Child, so Child's show() runs. It prints "Child show" then calls super.show(), which prints "Parent show".

❓ Predict Output

intermediate

Return type covariance in method overriding

What will be the output when this Java code runs?

Java

class Animal {}
class Dog extends Animal {}

class Parent {
    Animal getAnimal() {
        System.out.println("Parent getAnimal");
        return new Animal();
    }
}

class Child extends Parent {
    @Override
    Dog getAnimal() {
        System.out.println("Child getAnimal");
        return new Dog();
    }
}

public class Test {
    public static void main(String[] args) {
        Parent p = new Child();
        Animal a = p.getAnimal();
    }
}

A Child getAnimal\n

B Parent getAnimal\n

C Compilation error due to return type mismatch

D Runtime error

💡 Hint

Check if the return type in Child is allowed to be a subclass of Parent's return type.

Java allows covariant return types in overriding. Child's getAnimal returns Dog, a subclass of Animal, so it compiles and runs. The overridden method in Child is called, printing "Child getAnimal".

❓ Predict Output

advanced

Access modifier rules in method overriding

What error or output occurs when compiling and running this code?

Java

class Parent {
    protected void display() {
        System.out.println("Parent display");
    }
}

class Child extends Parent {
    @Override
    void display() {
        System.out.println("Child display");
    }
}

public class Test {
    public static void main(String[] args) {
        Parent p = new Child();
        p.display();
    }
}

A Runtime error

B Child display

C Parent display

D Compilation error: attempting to assign weaker access privileges

💡 Hint

Check if the access modifier in Child's display is compatible with Parent's.

Parent's display is protected. Child's display has default (package-private) access, which is weaker. Java does not allow reducing visibility in overriding, so this causes a compilation error.

❓ Predict Output

advanced

Exception rules in overridden methods

What happens when compiling this code?

Java

class Parent {
    void process() throws Exception {
        System.out.println("Parent process");
    }
}

class Child extends Parent {
    @Override
    void process() throws RuntimeException {
        System.out.println("Child process");
    }
}

public class Test {
    public static void main(String[] args) {
        Parent p = new Child();
        try {
            p.process();
        } catch (Exception e) {
            System.out.println("Caught Exception");
        }
    }
}

A RuntimeException thrown at runtime

B Compilation error: overridden method throws broader exception

C Child process

D Caught Exception

💡 Hint

Check if RuntimeException is allowed as an overridden method exception.

Child's process throws RuntimeException, which is unchecked and allowed. The method runs and prints "Child process". No exception is thrown, so catch block is not executed.

🧠 Conceptual

expert

Which statement about method overriding is true?

Select the only true statement about method overriding in Java.

A An overriding method must have the same return type or a subtype of the overridden method's return type.

B An overriding method can have a more restrictive access modifier than the overridden method.

C Static methods can be overridden like instance methods.

D An overriding method can throw any checked exception regardless of the overridden method's exceptions.

💡 Hint

Think about access modifiers, exceptions, return types, and static methods rules.

In Java, overriding methods must have the same or covariant return type. Access modifiers cannot be more restrictive. Checked exceptions must be the same or narrower. Static methods are hidden, not overridden.