Why do I keep getting errors from Java in Matlab?

My Matlab R2018b is giving Java errors. I have searched a lot on the internet for a solution but am unable to find one that works.

When do the errors occur?

I found a few ways to reproduce the errors.

When I have a line of code that looks like:

a = 1

This will of course create an orange wavy line under the = sign, since I forgot the ; at the end of the line. When I hover over orange wavy line it should give a suggestion, but instead it gives an error:

Exception in thread "AWT-EventQueue-0": java.lang.NullPointerException
	at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:216)
	at com.mathworks.help.helpui.DocRoot.buildDocPageUrl(DocRoot.java:44)
	at com.mathworks.mlwidgets.help.CSHelpTopicMap.mapIdToUrl(CSHelpTopicMap.java:244)
	at com.mathworks.mlwidgets.help.CSHelpTopicMap.mapID(CSHelpTopicMap.java:234)
	at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.getMapID(MatlabDocUtils.java:88)
	at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.idHasExtendedHelp(MatlabDocUtils.java:83)
	at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.mlintTagHasExtendedHelp(MatlabDocUtils.java:99)
	at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils.access$200(MatlabDocUtils.java:16)
	at com.mathworks.mlwidgets.text.mcode.MatlabDocUtils$CodeAnalyzerDocHelper.hasExtendedHelp(MatlabDocUtils.java:148)
	at com.mathworks.widgets.text.mcode.analyzer.CodeAnalyzerMessageModel$CodeAnalyzerMessage.hasExtendedInformation(CodeAnalyzerMessageModel.java:177)
	at com.mathworks.widgets.text.layer.EditorTip.makeButtonPanel(EditorTip.java:402)
	at com.mathworks.widgets.text.layer.EditorTip.makeSingleMessageRow(EditorTip.java:377)
	at com.mathworks.widgets.text.layer.EditorTip.addShortMessageComponentsToPanel(EditorTip.java:257)
	at com.mathworks.widgets.text.layer.EditorTip.makeWholeTipComponent(EditorTip.java:244)
	at com.mathworks.widgets.text.layer.EditorTip.makeWholeTipComponentWithoutExtendedMessage(EditorTip.java:213)
	at com.mathworks.widgets.text.layer.EditorTip.setupBalloonTip(EditorTip.java:199)
	at com.mathworks.widgets.text.layer.EditorTip.show(EditorTip.java:504)
	at com.mathworks.widgets.text.MWToolTipSupport.makeAndShowTip(MWToolTipSupport.java:351)
	at com.mathworks.widgets.text.MWToolTipSupport.makeTip(MWToolTipSupport.java:253)
	at com.mathworks.widgets.text.MWToolTipSupport.makeTip(MWToolTipSupport.java:216)
	at com.mathworks.widgets.text.MWToolTipSupport.makeTipAtMouse(MWToolTipSupport.java:185)
	at com.mathworks.widgets.text.MWKit$MWBuildToolTipAction.actionPerformed(MWKit.java:1507)
	at com.mathworks.mde.editor.EditorMKit$EditorBuildToolTipAction.actionPerformed(EditorMKit.java:163)
	at org.netbeans.editor.BaseAction.actionPerformed(BaseAction.java:259)
	at org.netbeans.editor.ext.ToolTipSupport.updateToolTip(ToolTipSupport.java:413)
	at org.netbeans.editor.ext.ToolTipContext$1.updateToolTip(ToolTipContext.java:17)
	at org.netbeans.editor.ext.ToolTipSupport.setToolTipVisible(ToolTipSupport.java:449)
	at org.netbeans.editor.ext.ToolTipSupport.setToolTipVisible(ToolTipSupport.java:429)
	at org.netbeans.editor.ext.ToolTipSupport.actionPerformed(ToolTipSupport.java:758)
	at org.netbeans.editor.WeakTimerListener.actionPerformed(WeakTimerListener.java:63)
	at javax.swing.Timer.fireActionPerformed(Unknown Source)
	at javax.swing.Timer$DoPostEvent.run(Unknown Source)
	at java.awt.event.InvocationEvent.dispatch(Unknown Source)
	at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
	at java.awt.EventQueue.access$500(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.awt.EventQueue$3.run(Unknown Source)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
	at java.awt.EventQueue.dispatchEvent(Unknown Source)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
	at java.awt.EventDispatchThread.run(Unknown Source)
 

Hovering over the orange wavy underline of the following line of code

disp(sprintf('a = %d, b = %7.4f',a,b));

would give the same sort of error.

Strangely the suggestion for code like

cellfun('isempty',strfind(a,'b'))

does work.

The whole documentation also does not work. If I type, for instance:

doc plot

I will also get an error:

Error using doc>displayDocPage (line 171)
Java exception occurred:
java.lang.NullPointerException

	at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:197)

	at com.mathworks.help.helpui.DocRoot.buildUrl(DocRoot.java:186)

	at com.mathworks.help.helpui.DocRoot.buildDocSetItemUrl(DocRoot.java:59)

	at com.mathworks.mde.help.DocCommandHelpBrowserTask.getUrlToDisplay(DocCommandHelpBrowserTask.java:42)

	at com.mathworks.mde.help.JsHelpBrowser.doHelpBrowserTask(JsHelpBrowser.java:242)

	at com.mathworks.mde.help.JsHelpBrowser.doHelpBrowserTask(JsHelpBrowser.java:238)

	at com.mathworks.mde.help.JsHelpBrowser.showReferencePage(JsHelpBrowser.java:122)

	at com.mathworks.mlservices.MLHelpServices.showReferencePage(MLHelpServices.java:199)


Error in doc (line 125)
    if ~displayDocPage(possibleTopics) && ~showHelpwin(topic)

It seems ot me that there is something wrong with Java.

What have I done so far?

I have removed the contents of the folder:

C:\Users\<user>\AppData\Roaming\MathWorks\MATLAB\R2018b

The preferences were removed but the error persisted.

I have uninstalled Matlab completely, downloaded it again an re-installed it. The errors kept coming.

After this I installed Java manually and configured Matlab to use the new Java as discribed in:

https://mathworks.com/matlabcentral/answers/130359-how-do-i-change-the-java-virtual-machine-jvm-that-matlab-is-using-on-windows#answer_137572

This still made no difference.

Has anyone got any suggestions to solve this problem?

[Adam]

Have you tried removing all non-Mathworks code from your path when you did a re-install ({or without a reinstall)?

[Jens Ravesloot]

I removed all search paths except those beginning with:

C:\Program Files\MATLAB\R2018b\...  

Also I made sure that there a no other files in the search paths that are not from Mathworks. This still does not solve the problem.

[Jens Ravesloot]

Does there exist a function to restore or debug Java in Matlab and check if all its dependencies and libraries are correct?

[Adam]

This sounds like a problem you would be best to contact Mathworks Tech Support about using the 'Contact Us' link in the top right of this website.

[Adrien BARRET]

Hi,

I have the same error since one or two month.

Have you solved this issue?

[Jens Ravesloot]

This problem resolved itself. No idea how or why...