Method overriding in Ruby - Mini Project: Build & Apply

Method overriding

📖 Scenario: Imagine you are creating a simple program to describe different types of vehicles. Each vehicle can describe itself, but some vehicles have special ways to describe themselves.

🎯 Goal: You will build a small Ruby program that shows how a child class can change the behavior of a method inherited from its parent class by overriding it.

📋 What You'll Learn

Create a parent class called Vehicle with a method describe that prints a general description.

Create a child class called Car that inherits from Vehicle.

Override the describe method in Car to print a more specific description.

Create objects of both classes and call their describe methods to see the difference.

💡 Why This Matters

🌍 Real World

Method overriding is used in many programs to customize or extend the behavior of existing code without changing the original code.

💼 Career

Understanding method overriding is important for working with object-oriented programming, which is common in software development jobs.

1

Create the parent class with a method

Create a class called Vehicle with a method describe that prints exactly "This is a vehicle."

Ruby

# Define class Vehicle with method describe
# Your code here

Hint

Use class Vehicle to start and def describe to define the method.

2

Create a child class that inherits from Vehicle

Create a class called Car that inherits from Vehicle.

Ruby

class Vehicle
  def describe
    puts "This is a vehicle."
  end
end

# Define class Car that inherits from Vehicle
# Your code here

Hint

Use class Car < Vehicle to inherit from Vehicle.

3

Override the describe method in Car

Inside the Car class, override the describe method to print exactly "This is a car."

Ruby

class Vehicle
  def describe
    puts "This is a vehicle."
  end
end

class Car < Vehicle
  # Override describe method here
  # Your code here
end

Hint

Define def describe inside Car and use puts "This is a car.".

4

Create objects and call describe methods

Create an object vehicle of class Vehicle and an object car of class Car. Then call describe on both objects.

Ruby

class Vehicle
  def describe
    puts "This is a vehicle."
  end
end

class Car < Vehicle
  def describe
    puts "This is a car."
  end
end

# Create objects and call describe methods
# Your code here

Hint

Create objects with Vehicle.new and Car.new. Call describe on each.

Practice

1. What does method overriding in Ruby allow a child class to do?

easy

A. Prevent the parent class from being used

B. Create a new method with a different name

C. Change the behavior of a method inherited from the parent class

D. Automatically call all parent methods

Solution

1. Step 1: Understand method overriding concept

   Method overriding means a child class uses the same method name as the parent but changes its behavior.

2. Step 2: Identify the effect on behavior

   The child class method replaces the parent's method behavior when called on the child object.

3. Final Answer:

   Change the behavior of a method inherited from the parent class -> Option C

4. Quick Check:

   Method overriding = change inherited method behavior [OK]

Hint: Same method name in child changes parent method behavior [OK]

Common Mistakes:

• Thinking overriding creates a new method with a different name
• Believing it prevents parent class usage
• Assuming it calls all parent methods automatically

2. Which of the following is the correct way to override a method named greet in a Ruby child class?

easy

A. class Child < Parent\n def greet_child\n puts 'Hello from child'\n end\nend

B. class Child < Parent\n def greet\n puts 'Hello from child'\n end\nend

C. class Child < Parent\n def greet() puts 'Hello from child' end\nend

D. class Child < Parent\n def greet: puts 'Hello from child' end\nend

Solution

1. Step 1: Check method name matches exactly

   Overriding requires the child method to have the same name as the parent method, here 'greet'.

2. Step 2: Verify Ruby method syntax

   Ruby method definitions use def method_name followed by body and end. Multi-line with indentation is standard. Parentheses are optional, but def greet() puts ... end is valid syntax if properly formatted. Colon syntax is invalid.

3. Final Answer:

   class Child < Parent\n def greet\n puts 'Hello from child'\n end\nend -> Option B

4. Quick Check:

   Same method name + correct syntax = override [OK]

Hint: Use same method name and proper def/end syntax [OK]

Common Mistakes:

• Changing method name instead of overriding
• Using incorrect method definition syntax
• Adding colon after method name

3. What will be the output of this Ruby code?

class Parent
  def greet
    puts 'Hello from Parent'
  end
end

class Child < Parent
  def greet
    puts 'Hello from Child'
  end
end

obj = Child.new
obj.greet

medium

A. Hello from Child

B. Error: undefined method greet

C. No output

D. Hello from Parent

Solution

1. Step 1: Identify class hierarchy and method overriding

   Child class overrides the greet method of Parent with its own version.

2. Step 2: Determine which method is called

   Creating an instance of Child and calling greet calls the Child's version, printing 'Hello from Child'.

3. Final Answer:

   Hello from Child -> Option A

4. Quick Check:

   Child method overrides parent = Child output [OK]

Hint: Child instance calls overridden method, not parent's [OK]

Common Mistakes:

• Expecting parent method output
• Thinking no output occurs
• Assuming method is undefined

4. Find the error in this Ruby code that tries to override a method:

class Parent
  def speak
    puts 'Parent speaks'
  end
end

class Child < Parent
  def speak()
    puts 'Child speaks'
  end

medium

A. Cannot override methods with parentheses

B. Method name should be different

C. Parent class must be declared inside Child

D. Missing end for Child class

Solution

1. Step 1: Check class and method block endings

   The Child class is missing the closing end keyword to finish the class definition.

2. Step 2: Confirm method overriding syntax

   The method speak is correctly named and defined; parentheses are allowed but optional.

3. Final Answer:

   Missing end for Child class -> Option D

4. Quick Check:

   Every class needs matching end [OK]

Hint: Count your end keywords carefully [OK]

Common Mistakes:

• Thinking method name must change
• Believing parentheses cause error
• Confusing class nesting rules

5. Given this Ruby code, what will be the output?

class Animal
  def sound
    'Some sound'
  end
end

class Dog < Animal
  def sound
    super + ' and Bark'
  end
end

class Cat < Animal
  def sound
    super + ' and Meow'
  end
end

puts Dog.new.sound
puts Cat.new.sound

hard

A. Some sound and Bark\nSome sound and Meow

B. Some sound\nSome sound

C. and Bark\nand Meow

D. Error: super called incorrectly

Solution

1. Step 1: Understand use of super in overridden methods

   Both Dog and Cat override sound and call super to get Animal's sound return value.

2. Step 2: Combine parent and child method results

   Each child adds its own string to the parent's 'Some sound', resulting in 'Some sound and Bark' and 'Some sound and Meow'.

3. Final Answer:

   Some sound and Bark\nSome sound and Meow -> Option A

4. Quick Check:

   super adds parent method result [OK]

Hint: super calls parent method result to extend behavior [OK]

Common Mistakes:

• Ignoring super and expecting only child string
• Expecting error from super usage
• Thinking output is only parent's string