Running Eclipse-CDT on Ubuntu 18.04 causes java.lang.ClassNotFoundException - c++

Question

I am running a Virtual Machine of Ubuntu 18.04 via Oracle VirtualBox.
I need Eclipse (including cdt) for a c++ project. So I ran the following statement on the console:
sudo apt-get install eclipse eclipse-cdt g++
Then I waited until it finished installing. Afterwards, I tried to run Eclipse, which caused the following error:
An error has occurred. See the log file
/home/matthias/.eclipse/org.eclipse.platform_3.8_155965261/configuration/1540208856928.log
So, I checked the log file. It says the following:
!SESSION Mon Oct 22 13:38:43 CEST 2018
----------------------------------------- !ENTRY org.eclipse.equinox.launcher 4 0 2018-10-22 13:38:43.262 !MESSAGE
Exception launching the Eclipse Platform: !STACK
java.lang.ClassNotFoundException:
org.eclipse.core.runtime.adaptor.EclipseStarter at
java.base/java.net.URLClassLoader.findClass(URLClassLoader.java:466)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:566)
at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:499)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:626)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:584) at
org.eclipse.equinox.launcher.Main.run(Main.java:1438) at
org.eclipse.equinox.launcher.Main.main(Main.java:1414)
Unfortunately, I am an absolute beginner with Ubuntu, as well as c++. I have no idea what could cause this problem. Can anybody help me?

Answer 1

I found that on Ubuntu18.04 this is due to a packaging problem (debugged with the help of a talented coworker). The fix was to manually install files from the older libequinox-osgi-java_3.8.1-8 package, to keep packaging happy.
Locate and get the .deb file
Examine contents of package vs. the system for overlaps
Manually extract deb into '/'
Commands:
$ cd /tmp
$ wget http://archive.ubuntu.com/ubuntu/pool/universe/e/eclipse/libequinox-osgi-java_3.8.1-8_all.deb
$ dpkg -c /tmp/libequinox-osgi-java_3.8.1-8_all.deb
$ dpkg -L libequinox-osgi-java
$ cd /
$ sudo dpkg -x /tmp/libequinox-osgi-java_3.8.1-8_all.deb
Notes:
Here we see commands to show eclipse depends on eclipse-rcp, which depends on libequinox-osgi-java (>= 3.9.1), which are all installed:
$ lsb_release -rc
Release: 18.04
Codename: bionic
$ apt-rdepends eclipse 2>&1 | egrep '^eclipse-rcp|libequinox-osgi-java'
eclipse-rcp
Depends: libequinox-osgi-java (>= 3.9.1)
libequinox-osgi-java
$ dpkg-query -W eclipse eclipse-rcp libequinox-osgi-java
eclipse 3.8.1-11
eclipse-rcp 3.8.1-11
libequinox-osgi-java 3.9.1-1
These commands show that the out-of-the box eclipse stubbornly insists on loading the older osgi_3.8.1.dist.jar despite not being able to stat it or open it:
$ strace -f -e trace=file /usr/lib/eclipse/eclipse -debug -clean -initialize 2>&1 |
egrep '^Framework.located|file:.*osgi_3.*jar|stat.*osgi_3.*jar'
[pid 117096] stat("/usr/lib/eclipse/plugins/org.eclipse.osgi_3.8.1.dist.jar", 0x7f4f0ca95540) = -1 ENOENT (No such file or directory)
[pid 117096] stat("/usr/lib/eclipse/plugins/org.eclipse.osgi_3.8.1.dist.jar", 0x7f4f0ca954c0) = -1 ENOENT (No such file or directory)
[pid 117096] stat("/usr/lib/eclipse/plugins/org.eclipse.osgi_3.8.1.dist.jar", 0x7f4f0ca95550) = -1 ENOENT (No such file or directory)
[pid 117096] stat("/usr/lib/eclipse/plugins/org.eclipse.osgi_3.8.1.dist.jar", 0x7f4f0ca954d0) = -1 ENOENT (No such file or directory)
Framework located:
file:/usr/lib/eclipse/plugins/org.eclipse.osgi_3.8.1.dist.jar
...
The older package just happens to be the same package used in the Ubuntu16.04 eclipse packages. We tried a few different ways to force install both older and newer packages, etc. but this made packaging unhappy and the manual extract Just Worked(tm).