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Preparing Matlab to use psychWithJava

This section explains how to prepare Matlab for development with psychWithJava package. Setup involves two steps: Setting the JVM version and setting the javaclasspath variable. OS specific instructions are given in alphabetical order.

Step 1: Set the JVM version

Launch Matlab on your system and check the Java version. Type 
version -java
and press enter. If the reported Java version is not 1.6 but you prefer to use 1.6 then you will have to configure your system to make Matlab use version 1.6. This is explained here. I give the current instructions below, but for most recent instructions you should follow the link above. (if this setup does not properly work, try using JDK 5.0 instead of JDK 6.0. Some versions of Matlab and JDK 6.0 do not work together very well.)

Linux

  • First find out where your JVM is installed. This is where the run time environment is located. If you followed my instructions here, then the path should be 
    /opt/jdk1.6/jre

  • Next set the MATLAB_JAVA variable. Open a terminal and type 
    echo $SHELL
    and press enter. If the response indicates that you are using bash, type 
    export MATLAB_JAVA=<path to JVM>
    and press enter. If your shell is tcsh, type 
    setenv MATLAB_JAVA <path to JVM>
    and press enter. Then start matlab as usual and check whether Java version is now 6.0 (1.6). You may need to start Matlab from the same terminal as you set the MATLAB_JAVA environment variable. If you want to add the setting to your start up script so that you don't have to manually set it everytime you use Matlab you can put the above commands in your .bash_profile or .tcshrc file.

    Next: Goto "Step 2: Set the javaclasspath" below

    • Mac OS X

  • MATLAB always uses the default version of the JVM installed on the computer. By default Mac OS X uses the older 1.4 version. If you followed the instructions on the previous page your preferred version should be 6.0.
  • However if you don't want to install the most recent revision and/or change the system wide default version from 1.4 to 6.0, you must specify the JAVA_JVM_VERSION environment variable for Matlab. Open a terminal and find out your SHELL. More on how to find out your shell is here. If your shell is bash, type 
    export JAVA_JVM_VERSION=1.6
    and press enter. If your shell is tcsh type 
    setenv JAVA_JVM_VERSION 1.6
    and press enter. Remember to check that Java version is now 6.0 (1.6) from within Matlab, to do this start a new Matlab session. If you want to add the setting to your start up script so that you don't have to manually set it everytime you use Matlab you can put the above commands in your .bash_profile or .tcshrc file. More on start-up scripts.

    On OS X, the bash environment changes do not take effect in FInder. Therefore if you performed the above steps and started a new Matlab session by double clicking on the Matlab icon, the JVM changes you performed will not apply. To work around this inconvinience you have to start Matlab using Terminal and typing in the full path to the Matlab program. If you have set JDK 6.0 as the system wide default you don't have to worry about this issue.

    Next: Goto "Step 2: Set the javaclasspath" below

    • MS Windows 2000/XP

  • Open Control Panel
  • Click System
  • Choose the Advanced tab and then click the Environment Variables button.
  • You now can set (or add) the MATLAB_JAVA system environment variable to the path of your JVM.

    • Step 2: Set the javaclasspath

    You can use the classes of psychWithJava from any directory on your system. However, to do so you have to include the path to your java packages in the javaclasspath variable. In order to find class definitions, Matlab searches directories and files that are set in the javaclasspath variable. There are two ways of setting the javaclasspath in Matlab. One is static, other is dynamic. Static one sets the path permenantly until you change the settings. That is, you don't need to set the path every time you launch Matlab. Dynamic path is temparory and lives only during the session in which you set it.

    Setting the dynamic path

    The official instructions are given here. I will sketch the steps below, but I recommend to follow the above link for most accurate information.

  • Launch Matlab. Add the psychWithJava package into the javaclasspath. Type 
    javaaddpath <full_path_to_psychWithJava>
    and press enter. <full_path_to_psychWithJava> is the full path to the psychWithJava.jar file. For example /home/boyaci/javaClasses/psychWithJava.jar on Linux, or /Users/boyaci/javaClasses/psychWithJava.jar on Mac OS X, or or C:\XXX\javaClasses\psychWithJava.jar on MS Windows.

  • Make sure that the path is added to the classpath. To check the java classpath (in Matlab command window), type 
    javaclasspath
    and press enter. Names of all packages in the current java class path should be listed including psychWithJava package.

    • Setting the static path

    Search Mathworks' web page for official instructions. Here I will sketch the steps that worked last time I performed this step.

  • To make changes in the static path you have to edit the classpath.txt file. There may be two versions of that file: local and shared. If you edit the shared one it will affect all users who share the same MATLAB root directory. Local file can be found/created in your own startup directory. When MATLAB starts up, it looks for classpath.txt first in your startup directory, and then in the default location. It uses the file it finds first. To see which classpath.txt file is currently being used by your MATLAB environment, launch Matlab and type 
    which classpath.txt
    press enter.

  • Edit the classpath.txt file either with Matlab editor or with another editor of your choice on your system. (On Linux or Mac OS X you may have to have administrative previliges to edit the shared classpath.txt file.) Add the full path to the psychWithJava.jar file. For example /home/XXX/javaClasses/psychWithJava.jar on Linux, or /Users/XXX/javaClasses/psychWithJava.jar on Mac OS X, or or C:\XXX\javaClasses\psychWithJava.jar on MS Windows.

  • Exit from Matlab and re-launch it. Make sure that the <path_to_your_java_packages> is added in the javaclasspath. To check the java classpath (in Matlab command window), type 
    javaclasspath
    and press enter. Names of all packages in the current java class path should be listed including psychWithJava package.

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