Cannot call java class from Matlab

Hi all. I have a peculiar problem. I am trying to use a java class in Matlab. I have made a very simple java Hello World example:

public class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }
}

After compiling (using jdk1.7.0_04 - the 64 bit version), I use the javaaddpath to direct Matlab to the custom class folder, in my case 'c:\temp\javaclass\' so I write:

javaaddpath('c:\temp\javaclass\')

I then try to create an object

Hello = HelloWorldApp()

but I get the error

Undefined function or variable 'HelloWorldApp'.

I have spent hours now trying to figure it out, I've read the tutorial sevaral times, I have tried looking for answers at Mathworks Answers, but nothing has helped so far. Can anyone point out the reason for my failure?

Answer 1

[Oleg Komarov]

I tried your example but I added the path manually to $matlabroot\toolbox\local\classpath.txt (on a new line simply add):

C:\java\

Then start MATLAB and check the path with javaclasspath.

Finally call HelloWorldApp

Warning: A Java exception occurred trying to load the HelloWorldApp class:
Java exception occurred:
java.lang.UnsupportedClassVersionError: HelloWorldApp : Unsupported major.minor
version 51.0

  at java.lang.ClassLoader.defineClass1(Native Method)

  at java.lang.ClassLoader.defineClass(Unknown Source)

  at java.security.SecureClassLoader.defineClass(Unknown Source)

  at java.net.URLClassLoader.defineClass(Unknown Source)

  at java.net.URLClassLoader.access$000(Unknown Source)

  at java.net.URLClassLoader$1.run(Unknown Source)

  at java.security.AccessController.doPrivileged(Native Method)

  at java.net.URLClassLoader.findClass(Unknown Source)

  at java.lang.ClassLoader.loadClass(Unknown Source)

  at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)

  at java.lang.ClassLoader.loadClass(Unknown Source)

  at java.lang.ClassLoader.loadClassInternal(Unknown Source)

  at java.lang.Class.forName0(Native Method)

  at java.lang.Class.forName(Unknown Source)

  at
    com.mathworks.jmi.OpaqueJavaInterface.findClass(OpaqueJavaInterface.java:470)

[Tobias Elmøe]

Problem solved: it was a wrong version of the jdk (1.7.0_04). After installing version 1.6.0_31 and compiling again, I was able to add the java object, after adding invoking the javaaddpath command first.

Hurray for totally obscurred (non)error messages. That cost me 3 hours of frustration.

[Oleg Komarov]

This technical note shows how to use the latest java version:

http://www.mathworks.co.uk/support/solutions/en/data/1-1812J/

[Titus Edelhofer]

Indeed, MATLAB uses a 1.6.x version of Java, so you need to use some 1.6.x as well (as you did 1.6.0_31).