Class definition syntax in MATLAB - Cheat Sheet & Quick Revision

Recall & Review

beginner

What keyword starts a class definition in MATLAB?

The keyword <code>classdef</code> is used to start a class definition in MATLAB.

beginner

How do you define properties inside a MATLAB class?

Properties are defined inside a properties block within the classdef. For example:

properties
  PropertyName
end

beginner

Where do you put methods in a MATLAB class?

Methods are placed inside a methods block within the classdef. For example:

methods
  function obj = MyClass()
    % constructor code
  end
end

beginner

What is the basic structure of a MATLAB class definition?

A MATLAB class starts with <code>classdef ClassName</code>, followed by <code>properties</code> and <code>methods</code> blocks, and ends with <code>end</code>. Example:<br><pre>classdef MyClass
  properties
    Prop1
  end
  methods
    function obj = MyClass()
    end
  end
end</pre>

intermediate

Can a MATLAB class have multiple methods blocks?

Yes, MATLAB allows multiple <code>methods</code> blocks in a class definition, which can be used to organize methods by access or other attributes.

Which keyword is used to define a class in MATLAB?

A classdef

B defclass

C class

D defineclass

The correct keyword to start a class definition in MATLAB is classdef.

Where do you define properties in a MATLAB class?

A Inside a <code>methods</code> block

B Inside a <code>properties</code> block

C Outside the classdef

D Inside a <code>functions</code> block

Properties are defined inside a properties block within the class.

What keyword ends a MATLAB class definition?

A end

B finish

C endclass

D stop

The end keyword is used to close the class definition.

Can you have more than one methods block in a MATLAB class?

A No, only one methods block is allowed

B Only if they are nested

C Yes, multiple methods blocks are allowed

D Only if they are static methods

MATLAB allows multiple methods blocks to organize methods.

Which of the following is a correct minimal MATLAB class definition?

A defclass MyClass end

B class MyClass endclass

C classdef MyClass()

D classdef MyClass end

A minimal MATLAB class uses classdef ClassName and ends with end.

Describe the basic syntax structure to define a class in MATLAB.

Think about how you start and end the class and where you put properties and methods.

Explain how properties and methods are organized inside a MATLAB class definition.

Consider the blocks inside the classdef and what goes where.

Practice

1. Which keyword is used to start a class definition in MATLAB?

easy

A. class

B. classdef

C. defineclass

D. objectdef

Solution

1. Step 1: Recall MATLAB class syntax

   In MATLAB, classes always start with the keyword classdef.

2. Step 2: Compare options

   Only classdef uses classdef, the correct keyword for defining classes.

3. Final Answer:

   classdef -> Option B

4. Quick Check:

   Class start keyword = classdef [OK]

Hint: Remember: MATLAB classes start with 'classdef' keyword [OK]

Common Mistakes:

• Using 'class' instead of 'classdef'
• Confusing with other languages' syntax
• Forgetting to use any keyword

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

easy

A. attributes
x
end

B. property
x
end

C. properties
x
end

D. props
x
end

Solution

1. Step 1: Recall properties block syntax

   In MATLAB, class data members are defined inside a properties block.

2. Step 2: Check each option

   Only properties x end uses the correct keyword properties to define data.

3. Final Answer:

   properties block -> Option C

4. Quick Check:

   Data inside 'properties' block [OK]

Hint: Use 'properties' keyword to define class data [OK]

Common Mistakes:

• Using 'property' instead of 'properties'
• Using 'props' or 'attributes' which are invalid
• Placing properties outside the classdef block

3. What will be the output of this MATLAB code?

classdef MyClass
    properties
        Value = 10;
    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(25);
disp(obj.getValue());

medium

A. 25

B. 10

C. Error: Cannot assign value

D. 0

Solution

1. Step 1: Understand property initialization

   The property Value starts at 10.

2. Step 2: Follow method calls

   The method setValue sets Value to 25, then getValue returns it.

3. Final Answer:

   25 -> Option A

4. Quick Check:

   Value updated to 25 and displayed [OK]

Hint: Setter updates property; getter returns updated value [OK]

Common Mistakes:

• Forgetting to assign returned object from setter
• Expecting initial value instead of updated
• Assuming direct property change without methods

4. Identify the error in this MATLAB class definition:

classdef Sample
    properties
        Data
    end
    methods
        function obj = Sample(val)
            Data = val;
        end
    end
end

medium

A. Missing semicolon after Data property

B. Incorrect classdef keyword usage

C. Properties block should be inside methods

D. Constructor does not assign value to object property

Solution

1. Step 1: Check constructor assignment

   The constructor assigns val to Data without obj., so it does not update the object property.

2. Step 2: Understand correct assignment

   It should be obj.Data = val; to update the property.

3. Final Answer:

   Constructor does not assign value to object property -> Option D

4. Quick Check:

   Use 'obj.Data = val;' in constructor [OK]

Hint: Use 'obj.Property = value;' inside methods [OK]

Common Mistakes:

• Assigning property without 'obj.' prefix
• Placing properties inside methods block
• Missing constructor function name matching class

5. How can you define a MATLAB class with a property Count that starts at 0 and a method increment that adds 1 to Count each time it is called? Choose the correct complete class definition.

hard

A. classdef Counter
properties
Count = 0;
end
methods
function obj = increment(obj)
obj.Count = obj.Count + 1;
end
end
end

B. classdef Counter
properties
Count;
end
methods
function increment(obj)
Count = Count + 1;
end
end
end

C. classdef Counter
properties
Count = 0;
end
methods
function increment(obj)
obj.Count = obj.Count + 1;
end
end
end

D. classdef Counter
properties
Count = 0;
end
methods
function obj = increment(obj)
Count = Count + 1;
end
end
end

Solution

1. Step 1: Initialize property correctly

   The property Count must start at 0, so initialize it as Count = 0;.

2. Step 2: Define method with object output and update property

   The method increment must accept and return the object (obj) and update obj.Count by adding 1.

3. Step 3: Check each option

   classdef Counter
       properties
           Count = 0;
       end
       methods
           function obj = increment(obj)
               obj.Count = obj.Count + 1;
           end
       end
   end

   correctly initializes Count, defines increment with obj input/output, and updates obj.Count. Others miss one or more of these.

4. Final Answer:

   Option A is the correct full class definition -> Option A

5. Quick Check:

   Property init + method with obj input/output =

   classdef Counter
       properties
           Count = 0;
       end
       methods
           function obj = increment(obj)
               obj.Count = obj.Count + 1;
           end
       end
   end

   [OK]

Hint: Methods changing properties must return updated object [OK]

Common Mistakes:

• Not returning updated object from method
• Updating property without 'obj.' prefix
• Not initializing property value