problem in compile time when using "var" in jdk 11

Roy Ash :

when I use the word "var" the IDE recognize the command, but when I compile the code, it gives me an error:

Error:(10, 17) java: cannot find symbol

symbol: class var

location: class Exp

the code:

public final class Exp
{
    public static void main(final String[] args)
    {
        var x=5;
    }
}

So why does it happen? How can i solve it?

the pics:

Roy Ash :

Thanks to @Marv the solution was

Settings -> Build, Execution, Deployment -> Compiler -> Java Compiler

and raise the Project Bytecode version to 11. (I raised it from 8 to 11)

Pic: