Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class

When launching Database configuration assistant (DBCA) you may encounter this error. The “java.lang.NoClassDefFoundError” error encounter when it could not initialize class “sun.awt.X11.XToolkit”. 

This normally occur when launching Graphic user interface (GUI)

No protocol specified

Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11.XToolkit

at java.lang.Class.forName0(Native Method)

at java.lang.Class.forName(Class.java:264)

at java.awt.Toolkit$2.run(Toolkit.java:860)

at java.awt.Toolkit$2.run(Toolkit.java:855)

at java.security.AccessController.doPrivileged(Native Method)

at java.awt.Toolkit.getDefaultToolkit(Toolkit.java:854)

at com.jgoodies.looks.LookUtils.isLowResolution(LookUtils.java:484)

at com.jgoodies.looks.LookUtils.<clinit>(LookUtils.java:249)

at com.jgoodies.looks.plastic.PlasticLookAndFeel.<clinit>(PlasticLookAndFeel.java:135)

at java.lang.Class.forName0(Native Method)

at java.lang.Class.forName(Class.java:348)

at javax.swing.SwingUtilities.loadSystemClass(SwingUtilities.java:1879)

at javax.swing.UIManager.setLookAndFeel(UIManager.java:582)

at oracle.install.commons.util.Application.startup(Application.java:976)

at oracle.install.commons.flow.FlowApplication.startup(FlowApplication.java:181)

at oracle.install.commons.flow.FlowApplication.startup(FlowApplication.java:198)

at oracle.assistants.common.base.driver.AssistantApplication.startup(AssistantApplication.java:336)

at oracle.assistants.dbca.driver.DBConfigurator.startup(DBConfigurator.java:378)
at oracle.assistants.dbca.driver.DBConfigurator.main(DBConfigurator.java:513)

The main causes of the issue is
1. The DISPLAY variable is NOT set or value is not correct.
2. X Windows is not installed
3. Oracle user not added to ACL (Access Control List)

If launching from server make sure you have any X Windows software installed and install org-x11-apps.x86_64 package

If you are launching from a local workstation, make sure you have XGraphics software such as Exceed, VLC…etc tools installed. Then You can set DISPLAY by using below command

CSH
$ setenv DISPLAY <IP Address of workstation or server>:0

SSH or KSH
$ export DISPLAY=<IP Address of workstation or server>:0

In Some cases, users may face issue when installing Oracle software on Ubuntu or Linux environment.

>>> Could not execute auto check for display colors using command /usr/bin/xdpyinfo. Check if the DISPLAY variable is set. Failed <<<<

Some requirement checks failed. You must fulfill these requirements before

continuing with the installation,

Continue? (y/n) [n] Y

>>> Ignoring required pre-requisite failures. Continuing...
Preparing to launch Oracle Universal Installer from /tmp/OraInstall2019-08-01_12-17-01PM. Please wait ....oracle$:~$ No protocol specified
Exception in thread "main" java.lang.NoClassDefFoundError: Could not initialize class sun.awt.X11.XToolkit

In this scenario, verify weather JDK installed on the system or not using below command
$ java -version

If not installed then installing required JDK will resolve the issue. If the problem persists, then run below command by logging as root

$ xhost +

Switch back to Oracle user and run the installation.

Thanks,

https://oracleracexpert.com, Oracle ACE Pro