Today I would like to introduce guest blogger Roderick, who wishes to remain anonymous. Roderick discusses his experience with setting up Matlab to use the latest stable release of Java, namely JVM 1.7, a.k.a. Java 7.

Background and executive summary

I work in the team where I do a lot of research and prototyping with Matlab. The final production code is however coded by a separate development team in Java 7. When running back-tests on our models I have to either ensure my Matlab prototype exactly matches the Java behavior, or to call the Java production code directly. However, although Java 7 has been available since July 2011 ^[1], the latest official Matlab version (R2013a at this point) still uses the JVM 1.6 (Java 6), which does not allow calling Java 7 code directly. Today’s article contains my experience in trying to let Matlab use JVM 1.7 code.
I urge readers to consider the following before trying the hacks I’ve found:

• The hacks described below were found to work for Matlab R2012b and R2013a on Windows 64bit. Simulink or any Matlab toolboxes were not tested, nor any other operating systems (although I’ve found most solutions to work on Linux as well).
• The set of hacks is not complete; some issues remain in the setup of Matlab to use Java 7.
• As with all other undocumented Matlab features, they may break in future Matlab versions.
• A future Matlab version (possibly as close as the upcoming R2013b) might be updated use Java 7 natively – the hacks should only be used on versions that have JVM 1.6.

It is worth considering a number of alternatives before trying to setup Matlab with the JVM 1.7:

• Compiling the Java project using JDK 1.6 instead of JDK 1.7. If you have the source code for a project and no specific Java 7 features are being used in the code, you could simply recompile it using JDK 1.6 or even 1.5. This would be a more advisable approach than switching Matlab to use Java 7, and enable full backward compatibility on Matlab releases as old as R2007b (for 1.6) or R14 SP2 (for 1.5).
• Use Java Remote Method Invocation (Java RMI ^[2]). This enables using Java 6 Java code that calls the Java 7 code. It requires some more work starting off, but has the benefit of not needing to switch Matlab to use Java 7. Due to using a different Java virtual machine, it also prevents duplicate dependencies between Matlab and Java code, when a Java project depends on Java libraries on which Matlab also depends. If Java code relies on a different version than Matlab for such a library, this may give problems with the Java classloader that could result in Matlab being unable to add Jar-file(s) to the java classpath – this issue is solved by separating the Java 7 code to use an independent JVM. The Java RMI approach appears to be a longer-term solution than hacking Matlab to use JVM 1.7.

If after considering the alternatives you have a valid use-case for Matlab to call Java 7 code, follow these steps:

1. Download the latest Matlab release if you can; earlier releases have more issues with JVM 1.7
2. Setup Matlab to use JVM 1.7
3. Create a startup function to detect if JVM 1.7 is used; if so, update the default figure’s CreateFcn to force visibility and then use drawnow
4. Enable the UseOldFileDialogs feature
5. Copy and patch listdlg.m to remove the hardcoded figure CreateFcn callback override
6. Copy and patch gui_mainfcn.m to force visibility of GUI objects by using uistack and by recursively flipping the order of all Children property, or by using the supplied code below

The text below details these steps.

Switching Matlab to use the JVM 1.7

To run Java 7 code from Matlab, Matlab needs to use JVM 1.7. To do this, see this MathWorks page ^[3], or follow these steps:

1. Ensure that you are using Java 6 or earlier – no need to do anything if your Matlab already has Java 7

   >> version -java
   ans =
   Java 1.6.0_17-b04 with Sun Microsystems Inc. Java HotSpot(TM) 64-Bit Server VM mixed mode
   

2. Download and install JRE 1.7 or JDK 1.7 from the Oracle website ^[4]
3. Create a new System Environment Variable called MATLAB_JAVA with the installation folder as its value. For example: “C:\Program Files\Java\jdk1.7.0_21\jre”
4. Restart Matlab and verify that it picked up the new Java version:

   >> version('-java')
   ans =
   Java 1.7.0_21-b11 with Oracle Corporation Java HotSpot(TM) 64-Bit Server VM mixed mode
   

Problems and workarounds with Matlab using JVM 1.7

Certain Matlab functionality was found to give issues when using the JVM 1.7. Most problems are related to visibility and display, although most Matlab code ran as-is without issue.

A) Matlab hangs after “Save As” or “Import Data”

Matlab hangs after clicking the <Import Data> button, or when trying to use the <Save As> functionality. This problem seems to be related to opening a certain type of window after which focus is not returned to Matlab. The user is forced to close Matlab via the Windows Task Manager. This problem was found in R2012b and earlier, however it seems fixed in R2013a. I have not found a solution for this problem; perhaps it is related to this issue ^[5]. Consider importing data via the command line, and first creating a new m-file then open it in the Matlab Editor. Alternatively, if you really get annoyed by this, you could use findobj functionality to disable the Matlab buttons.

B) Java exceptions from java.awt

Exceptions are occasionally thrown when multiple monitors are used, e.g. when moving figures from one screen to the other, or when docking figures. These exceptions can be a bit annoying, but they do not seem critical.

C) Matlab R2012b hangs using uigetfile

Matlab freezes when using uigetfile. It seems R2013a does not have this problem; for R2012b a solution was found by setting the undocumented UseOldFileDialogs feature ^[6]:

feature('UseOldFileDialogs', 1)

D) Defective Matlab dialog windows

Certain Matlab dialogs, such as questdlg, listdlg and inputdlg are missing some components. For example:

ButtonName = questdlg('What is your favorite color?', 'Color Question', 'Red', 'Green', 'Blue', 'Green');

set(0, 'DefaultFigureCreateFcn', @DefaultFigureCreationFcnForJVM7);
function DefaultFigureCreationFcnForJVM7(aObject, aEventdata)
    % PURPOSE: This function acts as the default figure create function to enforce focus for UI dialog objects % when using JVM 7.
    % IN:       - aObject (1x1 float): the handle to figure object
    %           - aEventdata (1x1 struct): the event data
    myDbStack = dbstack();
    if length(myDbStack) > 1 && any(strcmp(myDbStack(2).file, 'hgloadStructDbl.m'))
        % don't force visibility when GUIs are opened
    else
        set(aObject, 'Visible', 'on');
        drawnow();
    end

The UI dialogs flash a bit more when created, due to the fact that they resize and move around the screen for optimal placement. But at least they look ok now:

1. Find listdlg.m

   >> which listdlg
   C:\Program Files\MATLAB\R2013a\toolbox\matlab\uitools\listdlg.m
   

2. Copy listdlg.m to a personal folder and comment out the figure’s CreateFcn override in the copied file:

   fig_props = { ...
       'name'                   	figname ...
       'color'                  	get(0,'DefaultUicontrolBackgroundColor') ...
       'resize'                 	'off' ...
       'numbertitle'            	'off' ...
       'menubar'                	'none' ...
       'windowstyle'            	'modal' ...
       'visible'                	'off' ...
       ... % comment out the createfcn to empty such that we don't override the specific createfcn for JVM 1.7!
       ... %'createfcn'  	''    ...
       'position'               	fp   ...
       'closerequestfcn'        'delete(gcbf)' };
   

3. Similarly, copy the private functions getnicedialoglocation.m and setdefaultbutton.m and place their entire contents at the end of your copied listdlg.m.
4. Ensure that your personal folder is higher on the Matlab path than toolbox\matlab\uitools\

E) Custom GUI visibility problems

If you developed custom Matlab GUIs, you might notice visibility problems when opening the GUIs. For example, assume we have developed the following simple GUI:

myFigureHandle = TestGUI;
myChildHandles = get(myFigureHandle, 'Children')
set(myFigureHandle, 'Children', flipud(myChildHandles))

set(myChildHandles(1), 'Children', flipud(get(myChildHandles(1), 'Children')))

1. Locate gui_mainfcn.m

   >> which gui_mainfcn
   C:\Program Files\MATLAB\R2013a\toolbox\matlab\guide\gui_mainfcn.m
   

2. Copy gui_mainfcn.m to a personal folder and add a new call to a specific function for handling JVM7 issues for GUIs. The location of this function is important, put it just after the following feval command:

   ...
   feval(gui_State.gui_OpeningFcn, gui_hFigure, [], guidata(gui_hFigure), varargin{:});
   % Patched logic to ensure visibility of all objects
   HandleJvm7SupportForGUIs(gui_hFigure, guidata(gui_hFigure));
   ...
   

3. Place the following code at the end of your copied gui_mainfcn.m file:

   function HandleJvm7SupportForGUIs(aGUIObject, aGUIHandles)
       % PURPOSE: This function hacks around with the focus of objects on a GUI. It was found that GUIs do not
       % work as intended with the jvm 7 setup, and that objects on panels lose focus/visibility.
       % The approach which at is taken now is by flipping the order of childrens in uipanels.
       % Before the order is swapped, the panel is set to be the visible top-layer panel.
       % IN:       - aGUIObject (1x1 float): the handle the GUI figure
       %           - aGUIHandles (1x1 struct): the GUI handles
       if ~IsJvm7Used()
           return
       end
       myListOfHandleArrayFields = 'tabPanels';
       try
           set(aGUIObject, 'Visible', 'on');
           drawnow();
           if isprop(aGUIObject, 'Children')
               myChildren = get(aGUIObject, 'Children');
               myIsMenuItem = false(length(myChildren), 1);
               for i = 1:length(myChildren)
                   if isprop(myChildren(i), 'Type') && strcmp(get(myChildren(i), 'Type'), 'uimenu')
                       myIsMenuItem(i) = true();
                   end
               end
               myChildren(~myIsMenuItem) = flipud(myChildren(~myIsMenuItem));
               set(aGUIObject, 'Children', myChildren);
               drawnow();
           end
           myFields = fieldnames(aGUIHandles);
           myIsValid = true(size(myFields));
           for i = 1:length(myListOfHandleArrayFields)
               myIsValid = myIsValid & cellfun('isempty', strfind(myFields, myListOfHandleArrayFields{i}));
           end
           myFields = myFields(myIsValid);
           myPanelFields = {};
           for i = 1:length(myFields)
               if isprop(aGUIHandles.(myFields{i}), 'Type') && strcmp(get(aGUIHandles.(myFields{i}), 'Type'), 'uipanel')
                   myPanelFields =  [myPanelFields; myFields(i)]; %#ok
               end
           end
           for i = 1:length(myPanelFields)
               % allow three layers of panels maximum!
               if isprop(aGUIHandles.(myPanelFields{i}), 'Parent')
                   myParent = get(aGUIHandles.(myPanelFields{i}), 'Parent');
                   if strcmp(get(myParent, 'Type'), 'uipanel')
                       if isprop(myParent, 'Parent')
                           mySecondParent = get(myParent, 'Parent');
                           if strcmp(get(mySecondParent, 'Type'), 'uipanel')
                               uistack(mySecondParent, 'top');
                               drawnow();
                           end
                       end
                       uistack(myParent, 'top');
                       drawnow();
                   end
               end
               uistack(aGUIHandles.(myPanelFields{i}), 'top');
               drawnow();
               set(aGUIHandles.(myPanelFields{i}), 'Children', flipud(get(aGUIHandles.(myPanelFields{i}), 'Children')));
               drawnow();
           end
       catch myException
           disp(['WARN: could not initialize the GUI correctly with JVM 1.7 override logic, in ', mfilename()]);
           myException.getReport()
       end
   function theIsJvm7Used = IsJvm7Used()
       % PURPOSE: To indicate if Matlab is setup to use jvm 7
       % OUT:      - theIsJvm7Used (1x1 logical): whether or not JVM 7 is used
       myJavaVersion = version('-java');
       theIsJvm7Used = strcmpi(myJavaVersion(1:8), 'java 1.7');
   

4. Ensure that your personal folder is higher on the Matlab path than toolbox\matlab\uitools\

15 Comments To "Using Java 7 in Matlab R2013a and earlier"

#1 Comment By Malcolm Lidierth On June 20, 2013 @ 04:12

#2 Comment By Mike On July 3, 2013 @ 13:17

#3 Comment By kanmani On October 25, 2013 @ 21:19

#4 Comment By julien On January 14, 2014 @ 12:41

#5 Comment By Yair Altman On January 14, 2014 @ 12:53

#6 Comment By julien On January 14, 2014 @ 13:32

#7 Comment By Martin Lechner On April 2, 2014 @ 02:41

#8 Pingback By Java class access pitfalls | Undocumented Matlab On July 2, 2014 @ 08:34

#9 Comment By Wayan Permana On July 2, 2014 @ 18:15

Exception in thread "main" java.lang.UnsupportedClassVersionError: XBoxCox/SimultanBoxGraph : Unsupported major.minor version 51.0
	at java.lang.ClassLoader.defineClass1(Native Method)
	at java.lang.ClassLoader.defineClass(ClassLoader.java:616)
	at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
	at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
	at java.net.URLClassLoader.access$000(URLClassLoader.java:56)
	at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:303)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
	at java.lang.ClassLoader.loadClass(ClassLoader.java:248)
	at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:316)
	at tes.Tes11.main(Tes11.java:154)
Java Result: 1

#10 Comment By Yair Altman On July 3, 2014 @ 00:24

#11 Comment By Wayan Permana On July 3, 2014 @ 07:30

#12 Comment By Yair Altman On July 3, 2014 @ 12:58

#13 Comment By Fred On August 31, 2014 @ 15:56

#14 Comment By flo On August 6, 2015 @ 10:05

#15 Comment By Yair Altman On August 6, 2015 @ 11:29