Use java in matlab

Question

I encountered a problem when I tried to use java from matlab. I read through the tutorials from MathWork.com several times, also I re-installed the JDK1.6, in order to be compatible with matlab. However, after my work, it still doesn't work...

Here is the contents in classpath.txt:

 C:\Program Files\MATLAB\R2010a\java\jarext\xstream.jar C:\Program Files\MATLAB\R2010a\toolbox\javabuilder\jar\win64 \javabuilder.jar DYNAMIC JAVA PATH C:\Users\Gao\Desktop\connected_components_labeling

Clearly, the directory is included in the file. The connected_component_labeling is just a folder on my disk. The classes that I want to use in the connected_components_labeling are: Disjoint_Set.class and Node.class are in the connected_components_labeling folder.

I tried:

x = Disjoint_Set();

also

x = connected_components_labeling.Disjoint_Set();

None of them work. The only feedback I got from matlab is:

??? Undefined variable "connected_components_labeling" or class "connected_components_labeling.Disjoint_Set".

I'm pretty frustrated. Could anyone help me out? I'd appreciate it. Thanks a ton!

Is "connected_components_labeling" a package? Are the classes in a jar file? Or are they simply .class files sitting in that directory? Were those classes perhaps already in a package and then removed from it? — kelm
– kelm, Commented Jun 15, 2012 at 15:44
I just edited it. The connected_components_labeling is a package. The classes are not in a jar file. They are just .class files.Sorry for the confusion. — whileone
– whileone, Commented Jun 15, 2012 at 15:47
If connected_components_labeling is actually a package, it shouldn't be listed on the path. The directory that it lives in should be on the path instead. So the Desktop directory here. Probably not a great place for it. — kelm
– kelm, Commented Jun 15, 2012 at 15:52
@Gao: You should use javaaddpath to add entries to the Java class path — Amro
– Amro, Commented Jun 15, 2012 at 16:25
@Amro: I tried javaaddpath(). This function will add the files to dynamic path. And it also doesn't work. — whileone
– whileone, Commented Jun 15, 2012 at 17:22

Amro · Accepted Answer · 2012-06-15 18:18:37Z

Make sure that you are compiling the java files using a JRE/JDK that MATLAB is compatible with. As far as I can tell, MATLAB does not work properly with Java 7, so stick with Java 6 for the moment...

There are a couple of environment variables that affect MATLAB. In my case I have:

JAVA_HOME = C:\Program Files\Java\jdk1.6.0_32 MATLAB_JAVA = C:\Program Files\Java\jre6 PATH = ...;C:\Program Files\Java\jdk1.6.0_32\bin

Here is a simple test I just did:

C:\work\Student.java

public class Student { private String name; public Student(String str) { name = str; } public void setName(String str) { name = str; } public String getName() { return name; } public static void main(String args[]) { Student s = new Student("amro"); s.setName("unknown"); System.out.println("Hello " + s.getName()); } }

I compile: javac Student.java (the output is placed in the same directory c:\work\Student.class). Now I test it from MATLAB:

javaaddpath('C:\work') javaMethod('main','Student','') s = Student('me') char( s.getName() )

I get:

Hello unknown s = Student@8d6877 ans = me

+1 for checking that your JDK version is compatible with your MATLAB version. Fixed my problem. Thanks! Here's a list of supported JDK versions for each MATLAB version (click on the "Supported Compilers" link).
@FlorianBrucker: From what I understand there are workarounds.. But you don't have to worry about that anymore, you'll be happy to know that MATLAB R2013b finally upgraded to Java 7.

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