Handle vs value classes in MATLAB - Performance Comparison

Time Complexity: Handle vs value classes

O(n)

Understanding Time Complexity

When working with handle and value classes in MATLAB, it's important to understand how operations on these objects affect performance.

We want to see how the time to run code changes as we work with more objects or bigger data inside these classes.

Scenario Under Consideration

Analyze the time complexity of the following MATLAB code using handle and value classes.

classdef MyValueClass
    properties
        Data
    end
    methods
        function obj = MyValueClass(data)
            obj.Data = data;
        end
        function obj = updateData(obj, val)
            obj.Data = obj.Data + val;
        end
    end
end

classdef MyHandleClass < handle
    properties
        Data
    end
    methods
        function obj = MyHandleClass(data)
            obj.Data = data;
        end
        function updateData(obj, val)
            obj.Data = obj.Data + val;
        end
    end
end

% Usage example
n = 1000;
valObj = MyValueClass(zeros(1,n));
handleObj = MyHandleClass(zeros(1,n));
for i = 1:n
    valObj = valObj.updateData(i);
    handleObj.updateData(i);
end

This code defines two classes: one value class and one handle class, both updating data in a loop.

Identify Repeating Operations

Look at what repeats as the code runs.

• Primary operation: Loop runs n times, updating data inside objects.
• How many times: Each update happens once per loop iteration, so n times.
• Difference: Value class creates a new object each update, handle class modifies the same object.

How Execution Grows With Input

As n grows, the number of updates grows linearly.

Input Size (n)	Approx. Operations
10	10 updates
100	100 updates
1000	1000 updates

Each update takes roughly the same time, but value class updates involve copying data, which can add extra cost.

Final Time Complexity

Time Complexity: O(n)

This means the time to complete the updates grows directly with the number of updates.

Common Mistake

[X] Wrong: "Handle and value classes always have the same speed for updates because they run the same code."

[OK] Correct: Value classes copy the whole object on each update, which can slow things down, while handle classes change the same object without copying.

Interview Connect

Understanding how handle and value classes affect performance helps you write efficient MATLAB code and shows you know how object behavior impacts speed.

Self-Check

What if we changed the data inside the value class to a small scalar instead of a large array? How would the time complexity change?

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