[FIXED] Eclipse Launch Error Can't rurn simple program in Java

Issue

I am trying for past 3 hours to get and configure Eclipse IDE and I can't get what's wrong. I've been changing every single thing but can't make it work. Btw. I wanted to install Java SE 15... How can I resolve this?

I am getting this error when I am trying to build project:

Error: LinkageError occurred while loading main class org.sun.dem15
    java.lang.UnsupportedClassVersionError: Preview features are not enabled for org/sun/dem15 (class file version 59.65535). Try running with '--enable-preview'

UPDATE: After editing Project ---> Properties ----> Java Compiler and using --release option and enabling preview feature for Java 15 I got next error:

Errors occurred during the build.
Errors running builder 'Java Builder' on project 'demo'.
Provider "jar" not found

Solution

So, the problem was the most stupid thing in the world actually! And thing I would never suspect. Somehow Java SE 15 got problem, it "wasn't" installed on computer, even though I had directory in Program files which included all Java files(even the java wasn't installed)...

So you can check this actually by going into command prompt and typing: java -info and if you get:

'java' is not recognized as an internal or external command,
operable program or batch file

than the problem is your Java file isn't installed.

Also there's command javac -info and if you get same thing printed out in console still you don't have java se installed.

Answered By - Pshyotic