A simple alternative that does not require any Java is to use simple HTML. For example:

uicontrol('Style','popup', 'String',{'A', 'B
', 'C'});

Hi Yair,

Unfortunately, javacomponent did not solve the problem. The culprit is actually the renderer, as suggested here. After installing the java classes SeparatorComboBoxRenderer and SeparatorComboBoxListener therein (with slight adjustments), the following modification worked:

sep_txt    = '--------';
hPopup     = uicontrol('Style','popup','String',{'A','B',sep_txt,'C'});
%
jCombobox  = findjobj(hPopup);
jSeparator = javax.swing.JSeparator();
%
jCombobox.setRenderer(SeparatorComboBoxRenderer());
jCombobox.addActionListener(SeparatorComboBoxListener(jCombobox));
%
jCombobox.insertItemAt(jSeparator,2);
jCombobox.removeItemAt(3);  % this is required to keep the indices valid

A similar version with javax.swing.JComboBox and javacomponent also worked.

In any case, I thank you for the prompt response and the recommendation to work directly with java. It gave me the motivation to dig into some java code and find the solution.

Kindest regards, Yaroslav

@Yaroslav – instead of customizing the built-in Matlab uicontrol, create a standard javax.swing.JComboBox (where adding a JSeparator is easy), then add it to your figure window using javacomponent.

Do you know how to add a separator to a pop-up control (combo box)? I tried:

hPopup     = uicontrol('Style','popup','String',{'A','B','C'});
jCombobox  = findjobj(hPopup);
jSeparator = javax.swing.JSeparator(javax.swing.JSeparator.HORIZONTAL);
%
jCombobox.addItem(jSeparator);

But, alas, it didn’t work as expected (it added jSeparator.toString() instead). Where did I go wrong?

Kindest regards, Yaroslav

@Malcolm, I believe the OP does not dispute the fact that this is the expected behavior, he/she was simply asking whether there is any way to circumvent or modify this behavior. I do not know of any, but this is not saying that there isn’t any…

It is not a bug, it is expected behaviour

firstfunction accepts a copy of a MATLAB double array, modifies that copy and returns without altering anything in the MyClass instance.

secondfunction gets a reference to a java.lang.Double array as input- so MATLAB sees the changes made to that object

no…

http://stackoverflow.com/questions/5554518/can-matlab-not-read-back-a-double-array-from-java