MATLAB: How to access a Java inner class from Matlab

inner classjavaMATLAB

As described in this MathWorks support node, it is not straightforward to access inner Java classes from Matlab…

Best Answer

However, contrary to the answer provided by support, this is possible without writing custom wrappers!

If you are trying to get an inner class that's an Enum class, because you need the Enum values, chances are you can get away with something like (credit Bob Gilmore):

NORMAL = javaMethod('valueOf', 'javax.swing.JTable$PrintMode', 'NORMAL')

For trickier situations, the best I've come up with so far is:

InnerClass = java.lang.Class.forName('package.OuterClass$InnerClass', true, classloader);

In order to get a classloader object that knows how to find your InnerClass, the best I've come up with so far is to start with a trivially constructable object from the same package, get that instance's class, then get the classloader from that:

trivial_instance = package.TrivialClass();
TrivialClass = trivial_instance.getClass();
package_class_loader = TrivialClass.getClassLoader();

Hopefully there's a better way out there...

Once you have the InnerClass object you can call newInstance() on it to make an instance. If InnerClass is an Enum, you can also use getFields() to get a list of the possible values.

Related Solutions

MATLAB: Inheritance of classes inside a package

Hi Petr,

interesting, I haven't tried this. What works is to treat InnerClass as part of the package, i.e.

classdef OuterClass < package.InnerClass

Then it should work. Whether functions/classes inside the package should be "freed" from the necessity to do so, I don't know ... By the way: package directory should not be the working directory, that makes things more complicated then necessary.

Titus

MATLAB: How to create an instance of a Java public static nested class from inside MATLAB 7.13 (R2011b)

There are several ways this can be done. The following class Outer, which contains the public static nested class Inner, will be used to illustrate two possible ways:

 public class Outer { 
     public static class Inner {
         public int y;
         public Inner() {
             y = 1;
         }
         public Inner(int y) {
             this.y = y;
         }
     }
     public static Inner makeInner() {
         return new Inner();
     }
 }

Add a public static method that returns a new instance of the inner class.

in = Outer.makeInner();
in.getClass().toString()
ans =
class Outer$Inner

Use java.lang.Class.getClasses().

%%Create an Instance;
out = Outer(); 
%%Create a Class object
oc = out.getClass(); 
%%Create a Class[] containing  all the public classes defined within Outer.
oc_public = oc.getClasses();
%%Class object for Outer.Inner
inner_class =  oc_public(1); 
%%Call a zero argument constructor 
in1 = inner_class.newInstance();
%%Call a constructor with arguments
types = javaArray('java.lang.Class',1);
types(1) = java.lang.Integer.TYPE;
in2 = inner_class.getConstructor(types).newInstance(int32(5));

Best Answer

Related Solutions

MATLAB: Inheritance of classes inside a package

MATLAB: How to create an instance of a Java public static nested class from inside MATLAB 7.13 (R2011b)

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