I found a clue to change the session type of Gnome.. :

I edited the file  /etc/gdm/custom.conf ,
end  uncommented the row :
#WaylandEnable=false

...
After I made it, (now) I get 
Type=x11  (as output of loginctl show session 2 -p Type,)

but
as well this , the output that I get running the .sh script is the same..

-------------------
root@localhost Downloads]# ./netbeans-8.2-linux.sh
Configuring the installer...
Searching for JVM on the system...
Extracting installation data...
Running the installer wizard...
Can`t initialize UI
Running in headless mode

Exception: java.awt.HeadlessException thrown from the UncaughtExceptionHandler in thread "main"
-------------------

now need to find another way .....

On Sat, Apr 21, 2018 at 11:20 AM, Angelo Moreschini <mrangelo.fedora@gmail.com> wrote:
hi,

with java is OK . 
I downloaded all  together (jdk and NetBeans)   from the Oracle site... :

----------
[angelo_dev@localhost ~]$ java -version

openjdk version "1.8.0_31"
OpenJDK Runtime Environment (build 1.8.0_31-b13)
OpenJDK 64-Bit Server VM (build 25.31-b07, mixed mode)


[angelo_dev@localhost ~]$ javac -version

javac 1.8.0_31

----------

After I posted the previous message I learned more ,
and now I am about sure that the  problem come from the graphic environment of Linux...

After I Installed Fedora 27 I got to use a Wayland session of gnome, instead the usual X11 session :

if I do :
loginctl show session 2 -p Type,
I get
Type=wayland
instead that
Type=x11 (that is the value I get on computer where is Fedora 21)

Wyland is not good environment for running the graphical program that is used to install netBeans... (the .sh script)

So I am looking now how I can return to  session X11 inside Gnome...

On Sat, Apr 21, 2018 at 12:19 AM, Samuel Sieb <samuel@sieb.net> wrote:
On 04/20/2018 06:22 AM, Angelo Moreschini wrote:
[root@localhost Downloads]#*./netbeans-8.2-linux.sh <http://netbeans-8.2-linux.sh>*
Configuring the installer...
Searching for JVM on the system...
Extracting installation data...
*Running the installer wizard...*
*Can`t initialize UI
Running in headless mode*

*Exception: java.awt.HeadlessException thrown from the UncaughtExceptionHandler in thread "main"*
--------------------
This is a problem about the java environment ?
it can be also a problem with the graphical environment of fedora ... (?)

An application running as root can't access the display when using Wayland.

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