Method overriding in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to override the method display in the subclass.

Java

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

class Child extends Parent {
    @Override
    void [1]() {
        System.out.println("Child display");
    }
}

Drag options to blanks, or click blank then click option'

Aoutput

Bshow

Cprint

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different method name in the subclass.

Forgetting the @Override annotation (though optional, it helps).

The method name in the subclass must exactly match the method name in the parent class to override it.

2fill in blank

medium

Complete the code to call the overridden method from the subclass object.

Java

class Parent {
    void greet() {
        System.out.println("Hello from Parent");
    }
}

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

public class Test {
    public static void main(String[] args) {
        Child obj = new Child();
        obj.[1]();
    }
}

Drag options to blanks, or click blank then click option'

Agreet

BsayHello

Chello

Ddisplay

Attempts:

3 left

💡 Hint

Common Mistakes

Calling a method name that does not exist in the class.

Using the parent class method name incorrectly.

To call the overridden method, use the exact method name defined in the class, which is greet.

3fill in blank

hard

Fix the error in the method overriding by completing the method signature correctly.

Java

class Animal {
    void sound() {
        System.out.println("Animal sound");
    }
}

class Dog extends Animal {
    @Override
    public [1] sound() {
        System.out.println("Bark");
    }
}

Drag options to blanks, or click blank then click option'

Adouble

Bvoid

CString

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the return type in the overriding method.

Adding a return statement when the parent method returns void.

The return type of the overriding method must match the parent method's return type, which is void here.

4fill in blank

hard

Fill both blanks to override the method and call the parent class method inside the overriding method.

Java

class Vehicle {
    void start() {
        System.out.println("Vehicle started");
    }
}

class Car extends Vehicle {
    @Override
    void [1]() {
        super.[2]();
        System.out.println("Car started");
    }
}

Drag options to blanks, or click blank then click option'

Astart

Brun

Dbegin

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method names in override and super call.

Forgetting to call the parent method if needed.

The method name must be start to override, and super.start() calls the parent method.

5fill in blank

hard

Fill all three blanks to override the method with a parameter and call the parent method with the same parameter.

Java

class Printer {
    void print(String message) {
        System.out.println("Printer: " + message);
    }
}

class ColorPrinter extends Printer {
    @Override
    void [1](String [2]) {
        super.[3]([2]);
        System.out.println("ColorPrinter: " + [2]);
    }
}

Drag options to blanks, or click blank then click option'

Aprint

Bmessage

Dtext

Attempts:

3 left

💡 Hint

Common Mistakes

Using different method or parameter names.

Not passing the parameter to the parent method.

The method name is print, the parameter name is message, and the parent method is called with super.print(message).

Practice

1.

What is method overriding in Java?

easy

A. When a child class provides a new version of a method from its parent class

B. When a method calls itself repeatedly

C. When two methods have the same name but different parameters

D. When a method is hidden from other classes

Solution

1. Step 1: Understand method overriding concept

   Method overriding means a child class changes the behavior of a method inherited from its parent class.

2. Step 2: Compare options with definition

   When a child class provides a new version of a method from its parent class correctly describes this. When a method calls itself repeatedly is recursion, C is method overloading, D is incorrect.

3. Final Answer:

   When a child class provides a new version of a method from its parent class -> Option A

4. Quick Check:

   Method overriding = child changes parent method [OK]

Hint: Overriding means child changes parent's method behavior [OK]

Common Mistakes:

• Confusing overriding with overloading
• Thinking overriding changes method signature
• Mixing overriding with recursion

2.

Which of the following is the correct syntax to override a method in Java?

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

easy

A. private void show() { System.out.println("Child"); }

B. @Override void show() { System.out.println("Child"); }

C. void Show() { System.out.println("Child"); }

D. void show(int x) { System.out.println("Child"); }

Solution

1. Step 1: Check method signature and annotation

   To override, method name and parameters must match exactly. Using @Override annotation helps catch mistakes.

2. Step 2: Analyze options

   private void show() { System.out.println("Child"); } uses private access modifier, narrowing from package-private (not allowed for overriding; causes hiding). void show(int x) { System.out.println("Child"); } changes parameters (overloading). void Show() { System.out.println("Child"); } has method name mismatch ('Show' vs 'show' due to case sensitivity). @Override void show() { System.out.println("Child"); } matches method signature exactly and uses @Override correctly.

3. Final Answer:

   @Override void show() { System.out.println("Child"); } -> Option B

4. Quick Check:

   @Override + same signature = correct override [OK]

Hint: Use @Override and same method signature to override [OK]

Common Mistakes:

• Narrowing access modifier (e.g., to private)
• Changing method parameters (overloading instead)
• Method name case mismatch

3.

What will be the output of the following code?

class Parent {
    void greet() { System.out.println("Hello from Parent"); }
}
class Child extends Parent {
    @Override
    void greet() { System.out.println("Hello from Child"); }
}
public class Test {
    public static void main(String[] args) {
        Parent obj = new Child();
        obj.greet();
    }
}

medium

A. Hello from Parent

B. Compilation error

C. Runtime error

D. Hello from Child

Solution

1. Step 1: Understand dynamic method dispatch

   When a parent reference points to a child object, overridden methods in child are called at runtime.

2. Step 2: Trace the method call

   obj is Parent type but refers to Child instance. Calling greet() runs Child's version.

3. Final Answer:

   Hello from Child -> Option D

4. Quick Check:

   Parent ref + Child object calls Child method [OK]

Hint: Parent reference calls child's overridden method at runtime [OK]

Common Mistakes:

• Expecting parent method output
• Confusing compile-time and runtime method binding
• Thinking method overloading applies here

4.

Identify the error in the following code snippet:

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

medium

A. Method name case mismatch causes no overriding

B. Missing return type in Child class method

C. Cannot override a method without parameters

D. No error, code is correct

Solution

1. Step 1: Check method names carefully

   Parent method is 'display' (lowercase d), Child method is 'Display' (uppercase D). Java is case-sensitive, so these are different methods.

2. Step 2: Understand @Override annotation effect

   @Override expects exact match. Here, it causes a compile-time error because method names differ in case.

3. Final Answer:

   Method name case mismatch causes no overriding -> Option A

4. Quick Check:

   Method names must match exactly, including case [OK]

Hint: Method names must match case exactly to override [OK]

Common Mistakes:

• Ignoring case sensitivity in method names
• Assuming @Override is optional and ignoring errors
• Confusing overriding with overloading

5.

Consider the following classes:

class Animal {
    String sound() { return "Some sound"; }
}
class Dog extends Animal {
    @Override
    String sound() { return "Bark"; }
}
class Cat extends Animal {
    @Override
    String sound() { return "Meow"; }
}
public class Test {
    public static void main(String[] args) {
        Animal[] animals = {new Dog(), new Cat(), new Animal()};
        for (Animal a : animals) {
            System.out.println(a.sound());
        }
    }
}

What is the output of this program?

hard

A. Bark
Some sound
Meow

B. Some sound
Some sound
Some sound

C. Bark
Meow
Some sound

D. Compilation error due to array of different types

Solution

1. Step 1: Understand polymorphism with overridden methods

   Each object calls its own overridden sound() method at runtime, even if referenced as Animal.

2. Step 2: Trace the loop output

   Dog's sound() returns "Bark", Cat's returns "Meow", Animal's returns "Some sound".

3. Final Answer:

   Bark Meow Some sound -> Option C

4. Quick Check:

   Array of Animals calls each overridden sound() correctly [OK]

Hint: Array of parent type calls each child's overridden method [OK]

Common Mistakes:

• Expecting all calls to use parent method
• Thinking array cannot hold different subclass objects
• Confusing overriding with overloading