Integrate Simple MATLAB Function into Java Application

This example shows how to invoke a MATLAB^® method that generates a magic square in a Java^® application.

Files

MATLAB Function Location	matlabroot\toolbox\javabuilder\Examples\MagicSquareExample\MagicDemoComp\makesqr.m
Java Code Location	matlabroot\toolbox\javabuilder\Examples\MagicSquareExample\MagicDemoJavaApp\getmagic.java

Procedure

1. Copy the MagicSquareExample folder that ships with MATLAB to your work folder:

   copyfile(fullfile(matlabroot,'toolbox','javabuilder','Examples','MagicSquareExample'))

   At the MATLAB command prompt, navigate to the new MagicSquareExample\MagicDemoComp subfolder in your work folder.

2. Examine the makesqr.m function.

   function y = makesqr(x)
   y = magic(x);

   At the MATLAB command prompt, enter makesqr(5).

   The output is a 5-by-5 matrix.

       17    24     1     8    15
       23     5     7    14    16
        4     6    13    20    22
       10    12    19    21     3
       11    18    25     2     9

3. Create a Java package that encapsulates makesqr.m by using the Library Compiler app or compiler.build.javaPackage.

   Use the following information for your project:

   Package Name	magicsquare
   Class Name	magic
   File to Compile	makesqr.m

   For example, if you are using compiler.build.javaPackage, type:

   buildResults = compiler.build.javaPackage('makesqr.m', ...
       'PackageName','magicsquare', ...
       'ClassName','magic');

   For more details, see the instructions in Generate Java Package and Build Java Application.

4. Write source code for a Java application that accesses the MATLAB function.

   The sample application for this example is in MagicSquareExample\MagicDemoJavaApp\getmagic.java.

    getmagic.java

   /* Necessary package imports */
   import com.mathworks.toolbox.javabuilder.*;
   import magicsquare.*;
   
   /*
    * getmagic class computes a magic square of order N. The
    * positive integer N is passed on the command line.
    */
   class getmagic
   {
      public static void main(String[] args)
      {
         MWNumericArray n = null;   /* Stores input value */
         Object[] result = null;    /* Stores the result */
         magic theMagic = null;     /* Stores magic class instance */
   
         try
         {
            /* If no input, exit */
            if (args.length == 0)
            {
               System.out.println("Error: must input a positive integer");
               return;
            }
   
            /* Convert and print input value*/
            n = new MWNumericArray(Double.valueOf(args[0]),MWClassID.DOUBLE);
   
            System.out.println("Magic square of order " + n.toString());
   
            /* Create new magic object */
            theMagic = new magic();
   
            /* Compute magic square and print result */
            result = theMagic.makesqr(1, n);
            System.out.println(result[0]);
         }
         catch (Exception e)
         {
            System.out.println("Exception: " + e.toString());
         }
   
         finally
         {
            /* Free native resources */
            MWArray.disposeArray(n);
            MWArray.disposeArray(result);
            if (theMagic != null)
               theMagic.dispose();
         }
      }
   }
   

   The program does the following:

   • Creates an MWNumericArray array to store the input data

   • Instantiates a magic object

   • Calls the makesqr method, where the first parameter specifies the number of output arguments and the following parameters are passed to the function in order as input arguments

   • Uses a try-catch block to handle exceptions

   • Frees native resources using MWArray methods

5. In MATLAB, navigate to the MagicDemoJavaApp folder.

6. Copy the generated magicsquare.jar package into this folder.

   • If you used compiler.build.javaPackage, type:

     copyfile(fullfile('..','MagicDemoComp','magicsquarejavaPackage','magicsquare.jar'))

   • If you used the Library Compiler, type:

     copyfile(fullfile('..','MagicDemoComp','magicsquare','for_testing','magicsquare.jar'))

7. In a system command window, navigate to the PlotDemoJavaApp folder.

8. Compile the Java application using javac.

   • On Windows^®, execute this command:

     javac -classpath "matlabroot\toolbox\javabuilder\jar\javabuilder.jar";.\magicsquare.jar getmagic.java

   • On UNIX^®, execute this command:

     javac -classpath "matlabroot/toolbox/javabuilder/jar/javabuilder.jar":./magicsquare.jar getmagic.java

   Replace matlabroot with the path to your MATLAB or MATLAB Runtime installation folder. For example, on Windows, the path may be C:\Program Files\MATLAB\R2023b.

   For more details, see Compile and Run MATLAB Generated Java Application.

9. From the system command prompt, run the application.

   • On Windows, type:

     java -classpath .;"matlabroot\toolbox\javabuilder\jar\javabuilder.jar";.\magicsquare.jar getmagic 5

   • On UNIX, type:

     java -classpath .:"matlabroot/toolbox/javabuilder/jar/javabuilder.jar":./magicsquare.jar getmagic 5

   The application outputs a 5-by-5 magic square in the command window.

       17    24     1     8    15
       23     5     7    14    16
        4     6    13    20    22
       10    12    19    21     3
       11    18    25     2     9

10. To follow up on this example:

    • Try running the generated application on a different computer.

    • Try building an installer for the package using compiler.package.installer.

    • Try integrating a package that consists of multiple functions.