Exception in thread "AWT-EventQueue-0": java.lang.​NoClassDef​FoundError on command window.

I am new to Matlab, learning in Uni. I installed MATLAB from my University license. So, No matter what I type on Command window, the command does execute, but also this long error text in red. For example:

>> 1+1

ans =

     2

Exception in thread "AWT-EventQueue-0": java.lang.NoClassDefFoundError: Could not initialize class com.mathworks.mlwidgets.help.HelpPrefs
	at com.mathworks.mlwidgets.help.HelpUtils.isDocInstalled(HelpUtils.java:453)
	at com.mathworks.mde.functionhints.FunctionHints.openFunctionHints(FunctionHints.java:108)
	at com.mathworks.mde.cmdwin.CmdWinEditorKit.maybeOpenFunctionHints(CmdWinEditorKit.java:1706)
	at com.mathworks.mde.cmdwin.CmdWinEditorKit.access$1000(CmdWinEditorKit.java:88)
	at com.mathworks.mde.cmdwin.CmdWinEditorKit$CWDefaultKeyTypedAction.actionPerformed(CmdWinEditorKit.java:2175)
	at javax.swing.SwingUtilities.notifyAction(SwingUtilities.java:1668)
	at javax.swing.JComponent.processKeyBinding(JComponent.java:2882)
	at javax.swing.JComponent.processKeyBindings(JComponent.java:2929)
	at javax.swing.JComponent.processKeyEvent(JComponent.java:2845)
	at com.mathworks.mde.cmdwin.XCmdWndView.processKeyEvent(XCmdWndView.java:2461)
	at java.awt.Component.processEvent(Component.java:6316)
	at java.awt.Container.processEvent(Container.java:2239)
	at com.mathworks.mde.cmdwin.XCmdWndView.processEvent(XCmdWndView.java:439)
	at java.awt.Component.dispatchEventImpl(Component.java:4889)
	at java.awt.Container.dispatchEventImpl(Container.java:2297)
	at java.awt.Component.dispatchEvent(Component.java:4711)
	at java.awt.KeyboardFocusManager.redispatchEvent(KeyboardFocusManager.java:1954)
	at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(DefaultKeyboardFocusManager.java:835)
	at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(DefaultKeyboardFocusManager.java:1103)
	at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(DefaultKeyboardFocusManager.java:974)
	at java.awt.DefaultKeyboardFocusManager.dispatchEvent(DefaultKeyboardFocusManager.java:800)
	at java.awt.Component.dispatchEventImpl(Component.java:4760)
	at java.awt.Container.dispatchEventImpl(Container.java:2297)
	at java.awt.Window.dispatchEventImpl(Window.java:2746)
	at java.awt.Component.dispatchEvent(Component.java:4711)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:760)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:84)
	at java.awt.EventQueue$4.run(EventQueue.java:733)
	at java.awt.EventQueue$4.run(EventQueue.java:731)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:74)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:730)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:205)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

please help me fix it.

[Walter Roberson]

Sometimes it helps to delete the contents of your preferences directory and then restart MATLAB; https://www.mathworks.com/help/matlab/ref/prefdir.html

[Aayush Boliya]

that's not working, same errors.

[Walter Roberson]

I recommend you contact Mathworks for free installation support.

Mathworks Support will be closing for the weekend fairly soon, so you had best contact them immediately.

[VA]

Have you fixed, please show me, thank you

Answer 1

[Kautuk Raj]

I was also facing this issue and I fixed it by regenerating preferences in MATLAB.

You can follow this post on the MATLAB Answers forum for more details: https://www.mathworks.com/matlabcentral/answers/99625-how-do-i-regenerate-my-matlab-preferences