Handle vs value classes in MATLAB - Practice Questions

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of modifying a handle class object

Consider the following MATLAB code using a handle class. What will be the output after running the code?

MATLAB

classdef MyHandle < handle
    properties
        Value
    end
end

obj1 = MyHandle();
obj1.Value = 10;
obj2 = obj1;
obj2.Value = 20;
disp(obj1.Value);

A 20

B 10

C 0

D Error: Undefined property 'Value'

💡 Hint

Remember that handle classes share the same object reference.

In MATLAB, handle class objects are passed by reference. Assigning obj2 = obj1 makes obj2 refer to the same object as obj1. Changing obj2.Value changes obj1.Value as well.

❓ Predict Output

intermediate

Output of modifying a value class object

Consider the following MATLAB code using a value class. What will be the output after running the code?

MATLAB

classdef MyValue
    properties
        Value
    end
end

obj1 = MyValue();
obj1.Value = 10;
obj2 = obj1;
obj2.Value = 20;
disp(obj1.Value);

A 20

B 10

C 0

D Error: Undefined property 'Value'

💡 Hint

Value classes create copies when assigned.

Value class objects are copied when assigned. Changing obj2.Value does not affect obj1.Value.

🧠 Conceptual

advanced

Difference in behavior between handle and value classes

Which statement best describes the difference between handle and value classes in MATLAB?

A Both handle and value classes behave the same when assigned to new variables.

B Handle classes are copied on assignment; value classes share the same reference.

C Handle classes are passed by reference; value classes are passed by value (copied).

D Value classes cannot have properties; handle classes can.

💡 Hint

Think about what happens when you assign one object to another variable.

Handle classes behave like pointers; assigning them copies the reference. Value classes create a new copy on assignment.

❓ Predict Output

advanced

Effect of modifying a property inside a method for handle vs value classes

Given the following MATLAB classes and code, what will be the output after running the script?

MATLAB

classdef MyHandle < handle
    properties
        Value = 0;
    end
    methods
        function increment(obj)
            obj.Value = obj.Value + 1;
        end
    end
end

classdef MyValue
    properties
        Value = 0;
    end
    methods
        function obj = increment(obj)
            obj.Value = obj.Value + 1;
        end
    end
end

h = MyHandle();
v = MyValue();
h.increment();
v = v.increment();
disp([h.Value, v.Value]);

A [1 1]

B [1 0]

C [0 1]

D [0 0]

💡 Hint

Consider how methods modify properties in handle vs value classes.

The handle class method modifies the object directly in place. The value class method returns a modified copy, which is assigned back to v with v = v.increment(), updating v.

🔧 Debug

expert

Identify the error when mixing handle and value class assignments

What error will occur when running the following MATLAB code?

MATLAB

classdef MyHandle < handle
    properties
        Value
    end
end

classdef MyValue
    properties
        Value
    end
end

h = MyHandle();
h.Value = 5;
v = MyValue();
v.Value = h;
v.Value.Value = 10;

A Error: Index exceeds matrix dimensions

B Error: Attempt to reference field of non-structure array

C Error: Assignment to a property of a non-handle object

D No error

💡 Hint

Consider what happens when you assign a handle object to a value class property and then try to modify it.

No error occurs. A value class can store a handle class object in its property. Properties of the handle class object can be modified directly even through the value class property because handle classes support mutation.

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