Method overriding in Ruby - Step-by-Step Execution

Concept Flow - Method overriding

Define Parent Class with method

↓

Define Child Class overriding method

↓

Create Child object

↓

Call method on Child object

↓

Child's method runs, not Parent's

↓

End

The child class replaces the parent's method with its own version when called on a child object.

Execution Sample

Ruby

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

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

child = Child.new
child.greet

This code shows a child class overriding a method from its parent class and calling the new method.

Execution Table

Step	Action	Evaluation	Output
1	Define Parent class with greet method	Parent#greet defined
2	Define Child class inheriting Parent and override greet	Child#greet defined
3	Create Child object	child is instance of Child
4	Call greet on child	Calls Child#greet (overrides Parent#greet)	Hello from Child
5	End of execution	No more code to run

💡 Program ends after calling overridden method on child object

Variable Tracker

Variable	Start	After Step 3	Final
child	undefined	Child instance created	Child instance

Key Moments - 2 Insights

Why does calling greet on child run Child's method, not Parent's?

Because the child class defines its own greet method, it overrides the parent's version. See execution_table step 4 where Child#greet is called.

What if Child did not define greet method?

Then calling greet on child would run Parent's greet method, since child inherits it. This is shown by the absence of Child#greet in step 2.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, which method is called when child.greet runs?

A Both Parent#greet and Child#greet

B Parent#greet

C Child#greet

D No method is called

💡 Hint

Check the 'Evaluation' column at step 4 in execution_table

At which step is the child object created?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look at the 'Action' column for object creation in execution_table

If Child did not override greet, what would be the output at step 4?

A "Hello from Child"

B "Hello from Parent"

C No output

D Error

💡 Hint

Refer to key_moments about what happens if Child does not define greet

Concept Snapshot

Method overriding lets a child class replace a parent's method.
Define method in parent class.
Define same method name in child class.
Calling method on child runs child's version.
If child lacks method, parent's runs.
Used for customizing behavior in subclasses.

Full Transcript

This example shows method overriding in Ruby. First, a Parent class defines a greet method that prints a message. Then, a Child class inherits Parent and defines its own greet method, replacing the parent's. When we create a Child object and call greet on it, Ruby runs the Child's greet method, not the Parent's. This is method overriding: the child class changes the behavior of a method inherited from the parent. If the child did not define greet, calling greet on the child would run the parent's method instead. This lets subclasses customize or replace behavior from their parent classes.

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