Properties and methods in MATLAB - Mini Project: Build & Apply

Properties and methods

📖 Scenario: You are creating a simple MATLAB class to represent a bank account. This class will store the account holder's name and balance. You will add properties to hold this data and methods to deposit and withdraw money.

🎯 Goal: Build a MATLAB class called BankAccount with properties Owner and Balance. Add methods to deposit money and withdraw money from the account.

📋 What You'll Learn

Create a class named BankAccount

Add properties Owner and Balance

Add a method deposit that adds money to Balance

Add a method withdraw that subtracts money from Balance

Print the final balance after transactions

💡 Why This Matters

🌍 Real World

Bank accounts and many other real-world objects can be modeled using classes with properties and methods to manage their data and behavior.

💼 Career

Understanding how to define and use properties and methods in MATLAB classes is important for software development, data modeling, and engineering applications.

1

Create the class with properties

Create a MATLAB class named BankAccount with two public properties: Owner and Balance. Initialize Balance to 0.

MATLAB

classdef BankAccount
    properties
        Owner
        Balance = 0;
    end
end
% Your code here

Hint

Use classdef to define the class and properties block to add Owner and Balance.

2

Add deposit method

Inside the BankAccount class, add a public method named deposit that takes an input amount and adds it to the Balance property.

MATLAB

classdef BankAccount
    properties
        Owner
        Balance = 0;
    end
    methods
        function deposit(obj, amount)
            % Your code here
        end
    end
end

Hint

Define the deposit method inside a methods block. Use obj.Balance = obj.Balance + amount; to add money.

3

Add withdraw method

Add a public method named withdraw to the BankAccount class. It should take an input amount and subtract it from the Balance property.

MATLAB

classdef BankAccount
    properties
        Owner
        Balance = 0;
    end
    methods
        function deposit(obj, amount)
            obj.Balance = obj.Balance + amount;
        end
        function withdraw(obj, amount)
            % Your code here
        end
    end
end

Hint

Inside the withdraw method, subtract amount from obj.Balance.

4

Create object and show final balance

Create an object account of class BankAccount. Set account.Owner to 'Alice'. Deposit 1000 and withdraw 250 using the methods. Print the final balance using disp(account.Balance).

MATLAB

account = BankAccount;
account.Owner = 'Alice';
% Your code here

Hint

Create the object, set the owner, call deposit(1000), then withdraw(250), and finally display the balance.

Practice

1. In MATLAB, what is the main purpose of properties in a class definition?

easy

A. To define functions that perform actions

B. To create loops inside the class

C. To store data related to the object

D. To handle errors during execution

Solution

1. Step 1: Understand what properties represent

   Properties in MATLAB classes are used to hold data or attributes about the object.

2. Step 2: Differentiate properties from methods

   Methods are functions that act on the data, not the data itself.

3. Final Answer:

   To store data related to the object -> Option C

4. Quick Check:

   Properties = Data storage [OK]

Hint: Properties always hold data, methods perform actions [OK]

Common Mistakes:

• Confusing properties with methods
• Thinking properties are for functions
• Assuming properties handle errors

2. Which of the following is the correct way to define a method inside a MATLAB class?

easy

A. methods
function obj = setValue(obj, val)
obj.Value = val;
end
end

B. properties
function obj = setValue(obj, val)
obj.Value = val;
end
end

C. function setValue(obj, val)
obj.Value = val;
end

D. methods
obj.Value = val;
end

Solution

1. Step 1: Identify method block syntax

   Methods in MATLAB classes are defined inside a methods block.

2. Step 2: Check function definition inside methods

   The function must have the object as input and output if modifying properties.

3. Final Answer:

   methods function obj = setValue(obj, val) obj.Value = val; end end -> Option A

4. Quick Check:

   Methods block + function syntax = methods function obj = setValue(obj, val) obj.Value = val; end end [OK]

Hint: Methods go inside 'methods' block with function keyword [OK]

Common Mistakes:

• Placing functions inside properties block
• Omitting the methods keyword
• Not returning the modified object

3. Consider the following MATLAB class snippet:

classdef MyClass
  properties
    Value
  end
  methods
    function obj = setValue(obj, val)
      obj.Value = val;
    end
    function v = getValue(obj)
      v = obj.Value;
    end
  end
end

obj = MyClass();
obj = obj.setValue(10);
disp(obj.getValue());

What will be the output when this code runs?

medium

A. 0

B. obj.Value

C. Error: Undefined function or variable 'Value'

D. 10

Solution

1. Step 1: Understand method calls and property assignment

   The method setValue sets the property Value to 10 and returns the updated object.

2. Step 2: Check the output of getValue

   The getValue method returns the current value of the property Value, which is 10.

3. Final Answer:

   10 -> Option D

4. Quick Check:

   Property set and get returns 10 [OK]

Hint: Methods update and return object; get method returns stored value [OK]

Common Mistakes:

• Forgetting to assign returned object from setValue
• Expecting property access without method
• Confusing property name with variable

4. Identify the error in this MATLAB class method definition:

methods
  function setValue(obj, val)
    obj.Value = val;
  end
end

medium

A. The method must return the modified object

B. The method name is invalid

C. Properties block is missing

D. The function keyword is not allowed inside methods

Solution

1. Step 1: Check method signature for modifying properties

   In MATLAB, when a method modifies object properties, it must return the updated object.

2. Step 2: Identify missing return value

   The method setValue does not return obj, so changes won't persist.

3. Final Answer:

   The method must return the modified object -> Option A

4. Quick Check:

   Modify method must return object [OK]

Hint: Return updated object when changing properties [OK]

Common Mistakes:

• Not returning the object after modification
• Assuming properties change without return
• Confusing function keyword usage

5. You want to create a MATLAB class BankAccount with a property Balance and a method deposit that adds money to the balance only if the amount is positive. Which of the following method definitions correctly implements this?

hard

A. methods
function deposit(obj, amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

B. methods
function obj = deposit(obj, amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

C. methods
function obj = deposit(amount)
if amount > 0
obj.Balance = obj.Balance + amount;
end
end
end

D. methods
function obj = deposit(obj, amount)
obj.Balance = obj.Balance + amount;
end
end

Solution

1. Step 1: Check method signature for modifying object

   The method must accept the object and amount, and return the updated object.

2. Step 2: Verify condition for positive amount

   The method correctly adds amount only if it is greater than zero.

3. Step 3: Identify incorrect options

   methods function deposit(obj, amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end does not return the object, so changes won't persist. methods function obj = deposit(amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end misses the object input. methods function obj = deposit(obj, amount) obj.Balance = obj.Balance + amount; end end adds amount without checking if positive.

4. Final Answer:

   methods function obj = deposit(obj, amount) if amount > 0 obj.Balance = obj.Balance + amount; end end end -> Option B

5. Quick Check:

   Return updated object and check amount > 0 [OK]

Hint: Return object and check positive amount before adding [OK]

Common Mistakes:

• Not returning updated object
• Missing object input argument
• Not checking if amount is positive