Handle vs value classes in MATLAB - Hands-On Comparison

Handle vs Value Classes in MATLAB

📖 Scenario: Imagine you are managing a simple drawing application where you create shapes. Some shapes should behave like value copies (each copy is independent), and others should behave like handles (copies refer to the same object).

🎯 Goal: You will create two classes in MATLAB: one as a value class and one as a handle class. Then you will see how copying and modifying objects behave differently for each type.

📋 What You'll Learn

Create a value class called ValueShape with a property color.

Create a handle class called HandleShape with a property color.

Create an object of each class with initial color 'red'.

Copy each object to a new variable and change the color of the copy to 'blue'.

Print the colors of the original and copied objects to observe the difference.

💡 Why This Matters

🌍 Real World

Understanding handle vs value classes helps when designing software that manages objects like shapes, documents, or data models where you want to control whether copies share data or are independent.

💼 Career

Many engineering and scientific applications in MATLAB require managing data efficiently. Knowing handle and value classes is essential for writing clear, bug-free code that behaves as expected when objects are copied or passed around.

1

Create the Value Class

Create a MATLAB class file named ValueShape that defines a value class with a public property called color. Initialize the color property to 'red' in the constructor.

MATLAB

% Create a value class called ValueShape with a property color
classdef ValueShape
    properties
        color
    end
    methods
        function obj = ValueShape()
            % Your code here
        end
    end
end

Hint

Use classdef to define the class and set color inside the constructor method.

2

Create the Handle Class

Create a MATLAB class file named HandleShape that defines a handle class by inheriting from handle. Add a public property called color and initialize it to 'red' in the constructor.

MATLAB

classdef ValueShape
    properties
        color
    end
    methods
        function obj = ValueShape()
            obj.color = 'red';
        end
    end
end

% Create a handle class called HandleShape with a property color
classdef HandleShape < handle
    properties
        color
    end
    methods
        function obj = HandleShape()
            % Your code here
        end
    end
end

Hint

Use classdef HandleShape < handle to make a handle class and set color in the constructor.

3

Create Objects and Modify Copies

Create an object vShape of class ValueShape and an object hShape of class HandleShape. Then create copies vCopy and hCopy by assigning vShape and hShape respectively. Change the color property of vCopy and hCopy to 'blue'.

MATLAB

classdef ValueShape
    properties
        color
    end
    methods
        function obj = ValueShape()
            obj.color = 'red';
        end
    end
end

classdef HandleShape < handle
    properties
        color
    end
    methods
        function obj = HandleShape()
            obj.color = 'red';
        end
    end
end

% Create objects and copies, then change colors
vShape = ValueShape();
hShape = HandleShape();
% Your code here

Hint

Assign the objects to new variables and then change the color property of the copies.

4

Display Colors to See the Difference

Use disp to print the color property of vShape, vCopy, hShape, and hCopy to observe how the value and handle classes behave differently.

MATLAB

classdef ValueShape
    properties
        color
    end
    methods
        function obj = ValueShape()
            obj.color = 'red';
        end
    end
end

classdef HandleShape < handle
    properties
        color
    end
    methods
        function obj = HandleShape()
            obj.color = 'red';
        end
    end
end

vShape = ValueShape();
hShape = HandleShape();
vCopy = vShape;
hCopy = hShape;
vCopy.color = 'blue';
hCopy.color = 'blue';

% Print colors to see difference
% Your code here

Hint

Use disp(['variable = ', variable.color]) to print each color.

Practice

1. Which statement correctly describes the difference between handle and value classes in MATLAB?

easy

A. Handle classes share data between copies, while value classes keep data separate.

B. Value classes share data between copies, while handle classes keep data separate.

C. Both handle and value classes always share data between copies.

D. Both handle and value classes always keep data separate for each copy.

Solution

1. Step 1: Understand handle class behavior

   Handle classes in MATLAB share the same data when copied, meaning changes to one copy affect all copies.

2. Step 2: Understand value class behavior

   Value classes create independent copies, so changes to one copy do not affect others.

3. Final Answer:

   Handle classes share data between copies, while value classes keep data separate. -> Option A

4. Quick Check:

   Handle = shared, Value = separate [OK]

Hint: Remember: handle = shared data, value = independent copies [OK]

Common Mistakes:

• Confusing which class shares data
• Thinking both classes behave the same
• Assuming handle classes create independent copies

2. Which of the following is the correct way to define a handle class in MATLAB?

easy

A. classdef MyClass < handle
properties
Value
end
end

B. classdef MyClass
properties
Value
end
end

C. classdef MyClass < value
properties
Value
end
end

D. classdef MyClass < shared
properties
Value
end
end

Solution

1. Step 1: Identify handle class syntax

   In MATLAB, to create a handle class, the class must inherit from the built-in handle class using < syntax.

2. Step 2: Check options for correct inheritance

   classdef MyClass < handle properties Value end end correctly inherits from handle. Options A, B, and D either omit inheritance or use invalid base classes.

3. Final Answer:

   classdef MyClass < handle properties Value end end -> Option A

4. Quick Check:

   Handle class inherits from 'handle' keyword [OK]

Hint: Handle classes inherit from 'handle' keyword in classdef [OK]

Common Mistakes:

• Omitting '< handle' in class definition
• Using incorrect base class names
• Confusing handle with value class syntax

3. Consider the following MATLAB code:

classdef MyHandleClass < handle
    properties
        Data
    end
end

obj1 = MyHandleClass();
obj1.Data = 10;
obj2 = obj1;
obj2.Data = 20;
disp(obj1.Data);

What is the output?

medium

A. 10

B. 20

C. Error: Cannot assign obj2 to obj1

D. Empty output

Solution

1. Step 1: Understand handle class assignment

   Since MyHandleClass inherits from handle, obj2 = obj1 makes obj2 reference the same object as obj1.

2. Step 2: Trace property change effect

   Changing obj2.Data to 20 changes the shared object, so obj1.Data also becomes 20.

3. Final Answer:

   20 -> Option B

4. Quick Check:

   Handle class copies share data, so output is 20 [OK]

Hint: Handle class copies share data; changes reflect everywhere [OK]

Common Mistakes:

• Thinking obj1.Data remains 10 after obj2.Data change
• Expecting error on assignment
• Confusing handle with value class behavior

4. The following MATLAB code is intended to create two independent objects, but it does not. What is the error?

classdef MyValueClass < handle
    properties
        Data
    end
end

obj1 = MyValueClass();
obj1.Data = 5;
obj2 = obj1;
obj2.Data = 10;
disp(obj1.Data);

medium

A. MyValueClass should inherit from handle to share data.

B. MyValueClass should inherit from handle to create independent copies.

C. MyValueClass should inherit from handle to avoid independent copies.

D. MyValueClass should not inherit from handle to keep copies independent.

Solution

1. Step 1: Analyze class inheritance

   The class MyValueClass inherits from handle, making it a handle class that shares data between copies.

2. Step 2: Check object assignment behavior

   obj2 = obj1 references the same object. Changing obj2.Data affects obj1.Data, so copies are not independent.

3. Step 3: Identify the error

   To create independent copies, it should be a value class by not inheriting from handle.

4. Final Answer:

   MyValueClass should not inherit from handle to keep copies independent. -> Option D

5. Quick Check:

   Value classes = independent copies, no handle inheritance [OK]

Hint: Value classes must NOT inherit handle to keep copies independent [OK]

Common Mistakes:

• Thinking value classes must inherit handle
• Confusing inheritance effect on copy behavior
• Assuming handle inheritance creates independent copies

5. You want to design a MATLAB class to represent a shared configuration object that multiple parts of your program can modify and see updates immediately. Which class type should you choose and why?

hard

A. Use a value class, because copies keep data separate and avoid unintended side effects.

B. Use a value class, because it allows shared data between copies automatically.

C. Use a handle class, because copies share the same data and reflect changes immediately.

D. Use a handle class, because it creates independent copies that do not affect each other.

Solution

1. Step 1: Understand the requirement for shared updates

   The program needs a shared configuration object where changes by one part are seen by others immediately.

2. Step 2: Match requirement to class behavior

   Handle classes share data between copies, so changes to one copy affect all references. Value classes keep data separate, so changes do not propagate.

3. Final Answer:

   Use a handle class, because copies share the same data and reflect changes immediately. -> Option C

4. Quick Check:

   Shared updates need handle class [OK]

Hint: Shared data needs handle class for immediate update reflection [OK]

Common Mistakes:

• Choosing value class for shared data
• Misunderstanding copy behavior of handle classes
• Assuming value classes share data automatically