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Construct Object Arrays

Build Arrays in the Constructor

A class constructor can create an array by building the array and returning it as the output argument.

For example, the ObjectArray class creates an object array that is the same size as the input array. Then it initializes the Value property of each object to the corresponding input array value.

classdef ObjectArray
   properties
      Value
   end
   methods
      function obj = ObjectArray(F)
         if nargin ~= 0
            m = size(F,1);
            n = size(F,2);
            obj(m,n) = ObjectArray;
            for i = 1:m
               for j = 1:n
                  obj(i,j).Value = F(i,j);
               end
            end
         end
      end
   end
end

To preallocate the object array, assign the last element of the array first. MATLAB® fills the first to penultimate array elements with default ObjectArray objects.

After preallocating the array, assign each object Value property to the corresponding value in the input array F. To use the class:

  • Create 5-by-5 array of magic square numbers

  • Create a 5-by-5 object array

F = magic(5); 
A = ObjectArray(F);
whos
  Name      Size            Bytes  Class          Attributes

  A         5x5               304  ObjectArray              
  F         5x5               200  double   

Referencing Property Values in Object Arrays

Given an object array objArray in which each object has a property PropName:

  • Reference the property values of specific objects using array indexing:

    objArray(ix).PropName
  • Reference all values of the same property in an object array using dot notation. MATLAB returns a comma-separated list of property values.

    objArray.PropName
  • To assign the comma-separated list to a variable, enclose the right-side expression in brackets:

    values = [objArray.PropName]

For example, given the ObjProp class:

classdef ObjProp
   properties
      RegProp
   end
   methods
      function obj = ObjProp
         obj.RegProp = randi(100);
      end
   end
end

Create an array of ObjProp objects:

for k = 1:5
   objArray(k) = ObjProp;
end

Access the RegProp property of the second element of the object array using array indexing:

objArray(2).RegProp
ans =

    91

Assign the values of all RegProp properties to a numeric array:

propValues = [objArray.RegProp]
propValues =

    82    91    13    92    64

Use standard indexing operations to access the values of the numeric array. For more information on numeric arrays, see Matrices and Arrays.

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