MATLAB: Can I use MATLAB object-oriented class syntax to add methods to a Java class in MATLAB 7.3(R2006b)

MATLAB

In MATLAB 7.2 (R2006a) I was able to add additional methods to Java classes by creating a MATLAB class directory (@<classname>) and defining functions. This no longer appears to work in R2006b.

For example: I wish to add a 'build' method to the native Java class 'java.util.Hashtable'. In a base directory, I create an '@java.util.Hashtable' directory, and inside it I put a 'build.m' function. Working in the base directory, I create an object of class 'java.util.Hashtable', and then attempt to invoke the 'build' method of that object. This worked in R2006a, but in R2006b returns the error:

 ??? Undefined function or method 'build' for input arguments of type 'java.util.Hashtable'.

I would like to have MATLAB revert to the older behavior, as this was a very useful tool in working between Java and MATLAB.

Best Answer

The ability to use MATLAB object-oriented class syntax to add methods to a Java class is not available in MATLAB 7.3 (R2006b).

To work around this issue, you can create a new Java class that inherits from and extends the base class. Then create an object that is an instance of the extended class.

Related Solutions

MATLAB: Are the methods of the MATLAB class exposed from the compiled Java Class with MATLAB Builder JA

The ability to expose the methods of a MATLAB class is not currently available in MATLAB Builder JA.

To work around this issue, a wrapper MATLAB function for each method of the MATLAB Class can be created.

MATLAB: Are cell arrays converted to arrays of type java.lang.Object, rather than to a particular type, in MATLAB 7.2 (R2006a)

This is an error within the documentation for MATLAB 7.2 (R2006a) within the Calling Java from MATLAB section of the External Interfaces manual.

The documentation should read as follows:

"MATLAB automatically converts the cell array elements to java.lang.Object class objects. Note that in order for a cell array to be passed from MATLAB, the corresponding argument in the Java method signature must specify java.lang.Object or an array of java.lang.Object."

To pass an array to java, you can either manually create an array of objects of the correct type, or modify the Java method to accept arguments of type java.lang.Object.

1. For example to create a Java array of the appropriate type do the following:

jHarray = javaArray('java.util.Hashtable',4);
jHarray(1) = java.util.Hashtable;
jHarray(1).put('a',3);
jHarray(2) = java.util.Hashtable;
jHarray(2).put('a',12);
jHarray(3) = java.util.Hashtable;
jHarray(3).put('a',24);
jHarray(4) = java.util.Hashtable;
jHarray(4).put('a',36);
MatlabJavaBug.hello(jHarray);

2. Alternatively, you can convert the method to have the following signature. Before using the elements of the array, you will need to cast them to the appropriate class. For example the function header would be modified as follows:

 public static void hello(java.lang.Object hash[])

Best Answer

Related Solutions

MATLAB: Are the methods of the MATLAB class exposed from the compiled Java Class with MATLAB Builder JA

MATLAB: Are cell arrays converted to arrays of type java.lang.Object, rather than to a particular type, in MATLAB 7.2 (R2006a)

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