Inheritance in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of method overriding in MATLAB inheritance

Consider the following MATLAB classes and script. What is the output when the script runs?

MATLAB

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

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

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

A Error: Method sound not found

B Bark

C Some generic animal sound

D No output

💡 Hint

Think about which class's sound method is called when you create a Dog object.

The Dog class overrides the sound method of Animal. So calling sound on a Dog object prints 'Bark'.

❓ Predict Output

intermediate

Output of calling superclass method explicitly

What is the output of this MATLAB code?

MATLAB

classdef Vehicle
    methods
        function start(obj)
            disp('Vehicle started')
        end
    end
end

classdef Car < Vehicle
    methods
        function start(obj)
            disp('Car engine warming up')
            start@Vehicle(obj);
        end
    end
end

myCar = Car();
myCar.start();

A Car engine warming up

B

Vehicle started
Car engine warming up

C

Car engine warming up
Vehicle started

D Error: Invalid syntax for superclass method call

💡 Hint

Look at how the superclass method is called inside the subclass method.

The Car class's start method first displays 'Car engine warming up' then explicitly calls the Vehicle class's start method, which displays 'Vehicle started'.

🔧 Debug

advanced

Identify the error in MATLAB inheritance code

What error does this MATLAB code produce when run?

MATLAB

classdef Parent
    properties
        Name
    end
    methods
        function obj = Parent(name)
            obj.Name = name;
        end
    end
end

classdef Child < Parent
    methods
        function obj = Child(name)
            obj.Name = name;
        end
    end
end

c = Child('Alice');

A Error: No constructor for superclass Parent called in Child constructor

B No error, object created successfully

C Error: Property 'Name' is not accessible

D Error: Syntax error in class definition

💡 Hint

Think about how constructors work in inheritance in MATLAB.

The Child constructor does not call the Parent constructor explicitly. MATLAB requires calling the superclass constructor to properly initialize inherited properties.

📝 Syntax

advanced

Which option correctly defines a subclass constructor calling superclass constructor?

Which of the following MATLAB subclass constructors correctly calls the superclass constructor?

A

function obj = Child(name)
    obj = obj.Parent(name);
end

B

function obj = Child(name)
    obj.Name = name;
    Parent(name);
end

C

function obj = Child(name)
    obj = Parent(name);
end

D

function obj = Child(name)
    obj = obj@Parent(name);
end

💡 Hint

Look for the correct syntax to call superclass constructor in MATLAB subclass constructor.

Option D uses the correct syntax obj = obj@Parent(name); to call the superclass constructor. Other options are either invalid syntax or do not assign the object properly.

🚀 Application

expert

Determine the number of methods available to subclass object

Given these MATLAB classes, how many methods does an object of class Manager have access to?

MATLAB

classdef Employee
    methods
        function work(obj)
            disp('Working')
        end
        function report(obj)
            disp('Reporting')
        end
    end
end

classdef Manager < Employee
    methods
        function manage(obj)
            disp('Managing')
        end
    end
end

m = Manager();

A 3

B 1

C 2

D 4

💡 Hint

Count all methods defined in Manager and its superclass Employee.

The Manager class inherits work and report from Employee and defines its own method manage. So total methods accessible are 3.

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