Inheritance in MATLAB - Step-by-Step Execution

Concept Flow - Inheritance

Define Base Class

↓

Define Derived Class inherits Base

↓

Create Derived Object

↓

Access Base and Derived Properties/Methods

↓

Use or Override Base Methods

↓

Program Ends

Inheritance lets a new class use properties and methods from an existing class, adding or changing features.

Execution Sample

MATLAB

classdef Animal
  properties
    Name
  end
  methods
    function speak(obj)
      disp('Animal sound')
    end
  end
end

classdef Dog < Animal
  methods
    function speak(obj)
      disp('Woof!')
    end
  end
end

myDog = Dog();
myDog.Name = 'Buddy';
myDog.speak();

Defines a base class Animal and a derived class Dog that overrides the speak method, then creates a Dog object and calls speak.

Execution Table

Step	Action	Object State	Output
1	Define class Animal with property Name and method speak	No objects yet
2	Define class Dog inheriting Animal, override speak method	No objects yet
3	Create object myDog of class Dog	myDog.Name = '' (empty)
4	Set myDog.Name = 'Buddy'	myDog.Name = 'Buddy'
5	Call myDog.speak()	myDog.Name = 'Buddy'	Woof!
6	End of program	myDog.Name = 'Buddy'	Program ends

💡 Program ends after calling overridden speak method on Dog object

Variable Tracker

Variable	Start	After Step 3	After Step 4	Final
myDog.Name	undefined	'' (empty)	'Buddy'	'Buddy'

Key Moments - 2 Insights

Why does calling speak() on myDog print 'Woof!' and not 'Animal sound'?

Because Dog class overrides the speak method from Animal. See execution_table step 5 where myDog.speak() calls Dog's version.

Does myDog have access to the Name property defined in Animal?

Yes, inheritance lets Dog objects use properties from Animal. See variable_tracker showing myDog.Name being set and used.

Visual Quiz - 3 Questions

Look at the execution_table at step 4, what is the value of myDog.Name?

A '' (empty string)

B undefined

C 'Buddy'

D 'Animal'

💡 Hint

Check variable_tracker column 'After Step 4' for myDog.Name value

At which step does the speak method output 'Woof!'?

A Step 4

B Step 5

C Step 3

D Step 6

💡 Hint

See execution_table row for step 5 under Output column

If Dog did not override speak(), what would myDog.speak() output?

A 'Animal sound'

B Error: method not found

C 'Woof!'

D No output

💡 Hint

Inheritance means derived class uses base method if not overridden (see concept_flow)

Concept Snapshot

Inheritance in MATLAB:
- Use < to inherit: classdef Child < Parent
- Child class gets Parent's properties and methods
- Child can override Parent methods
- Create objects of Child to use combined features
- Calling overridden methods uses Child's version

Full Transcript

This example shows how inheritance works in MATLAB. We first define a base class Animal with a property Name and a method speak that prints 'Animal sound'. Then we define a derived class Dog that inherits from Animal and overrides the speak method to print 'Woof!'. We create an object myDog of class Dog, set its Name property to 'Buddy', and call speak. The output is 'Woof!' because Dog's speak method replaces Animal's. The variable myDog.Name is accessible because Dog inherits properties from Animal. This demonstrates how inheritance allows reuse and customization of code.

Practice

1. What does inheritance allow a subclass to do in MATLAB?

easy

A. Change MATLAB's built-in functions

B. Use properties and methods from a parent class

C. Run code without a main function

D. Create variables without declaring them

Solution

1. Step 1: Understand inheritance concept

   Inheritance means a subclass can use code from a parent class.

2. Step 2: Identify what subclass gains

   The subclass gets properties and methods from the parent class automatically.

3. Final Answer:

   Use properties and methods from a parent class -> Option B

4. Quick Check:

   Inheritance = reuse parent code [OK]

Hint: Inheritance means reuse parent class code [OK]

Common Mistakes:

• Thinking inheritance creates variables automatically
• Confusing inheritance with running code without main
• Believing inheritance changes built-in MATLAB functions

2. Which of the following is the correct way to declare a subclass Dog that inherits from superclass Animal in MATLAB?

easy

A. classdef Dog inherits Animal

B. classdef Dog : Animal

C. classdef Dog extends Animal

D. classdef Dog < Animal

Solution

1. Step 1: Recall MATLAB inheritance syntax

   MATLAB uses < symbol to indicate inheritance in classdef.

2. Step 2: Match correct syntax

   The correct syntax is classdef Dog < Animal.

3. Final Answer:

   classdef Dog < Animal -> Option D

4. Quick Check:

   Inheritance uses < in MATLAB [OK]

Hint: Use < to inherit in MATLAB classdef [OK]

Common Mistakes:

• Using 'inherits' keyword instead of <
• Using ':' or 'extends' which are not MATLAB syntax
• Confusing MATLAB syntax with other languages

3. Consider the following MATLAB code:

classdef Animal
    methods
        function sound(obj)
            disp('Some sound')
        end
    end
end

classdef Dog < Animal
    methods
        function sound(obj)
            disp('Bark')
        end
    end
end

myPet = Dog();
myPet.sound();

What will be the output when running myPet.sound()?

medium

A. Error: Method not found

B. Some sound

C. Bark

D. No output

Solution

1. Step 1: Understand method overriding in subclass

   The subclass Dog defines its own sound method, which replaces the superclass method.

2. Step 2: Determine which method runs

   Calling myPet.sound() runs the Dog version, printing 'Bark'.

3. Final Answer:

   Bark -> Option C

4. Quick Check:

   Subclass method overrides superclass method [OK]

Hint: Subclass method overrides superclass method [OK]

Common Mistakes:

• Expecting superclass method output
• Thinking both methods run
• Assuming error due to overriding

4. What is wrong with this MATLAB subclass definition?

classdef Cat <
    methods
        function meow(obj)
            disp('Meow')
        end
    end
end

medium

A. Missing superclass name after <

B. Method name cannot be 'meow'

C. Classdef keyword is misspelled

D. No constructor defined

Solution

1. Step 1: Check inheritance syntax

   The symbol < must be followed by the superclass name.

2. Step 2: Identify missing superclass

   Here, no superclass name is given after <, causing syntax error.

3. Final Answer:

   Missing superclass name after < -> Option A

4. Quick Check:

   Inheritance requires superclass name after < [OK]

Hint: Always specify superclass name after < [OK]

Common Mistakes:

• Leaving out superclass name after <
• Thinking method names cause error
• Assuming constructor is mandatory

5. You have a superclass Vehicle with a method move() that prints 'Moving'. You want to create a subclass Car that inherits Vehicle but adds a new method honk() that prints 'Beep!'. Which of the following is the correct MATLAB code for the subclass Car?

hard

A. classdef Car < Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

B. classdef Car inherits Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

C. classdef Car : Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

D. classdef Car extends Vehicle
methods
function honk(obj)
disp('Beep!')
end
end
end

Solution

1. Step 1: Use correct inheritance syntax

   MATLAB uses < to inherit, so classdef Car < Vehicle is correct.

2. Step 2: Add new method in subclass

   The method honk is added inside methods block correctly.

3. Final Answer:

   classdef Car < Vehicle with honk method -> Option A

4. Quick Check:

   Subclass syntax + new method = classdef Car < Vehicle methods function honk(obj) disp('Beep!') end end end [OK]

Hint: Use < and add methods block for new methods [OK]

Common Mistakes:

• Using 'inherits', ':', or 'extends' instead of <
• Forgetting to add methods block
• Trying to override without correct syntax