[Drjava-users] Current document is out of sync with the Interactions Pane and should be recompiled!

[Kevin R. B. <kbu...@at...>]

I struggled with getting DrJava to work.  It was used in a course I was
planning to take.  I worked a lot time to figure out how to get DrJava
to work, and I see that a number of other people over the years have
had basically the same problem, and they don't always seem to get
answers, so I figured blasting this information out on the mailing
list might be helpful if it makes one more place people have a
chance of finding something helpful.

In my case, I am using a Linux system that has both OpenJDK and a
manually installed Oracle JDK (extracted from a tarball obtained from
java.com), along with some other JRE environments in various places.
That said, I think basically the things I found might not necessarily
entirely be platform-specific even if some of the details are, so I
hope that even if a reader doesn't use Linux, if they read between
the lines, so to speak, something worth trying might become evident.

In any event, I "installed" DrJava by .jar file rather than by
the installer (`DrJava Version : drjava-20190813-220051`). I ran it
from the command-line `java -jar drjava-beta-20190813-220051.jar`.
I then clicked `[ Manual Download ]` when it asked about installing
updates (`drjava-beta-2019-220051`).

DrJava reported that my compiler was `JDK 8.0_222`.  Note, I don't know
where that compiler came from.  As far as I know, I didn't have that
version installed. My OpenJDK was:

    $ /bin/java -version
    openjdk version "1.8.0_252"
    OpenJDK Runtime Environment (build 1.8.0_252-b09)
    OpenJDK 64-Bit Server VM (build 25.252-b09, mixed mode)

I typed in a simple "Hello World" program, and every attempt to compile
produced:

    Compiler Output:
      "Compilation completed."

This is a bug, because in fact compilation apparently did not complete.

Clicking `Run` produced:

    Interactions
      Welcome to DrJava.  Working directory is
    /home/krb/Projects/Software/java Current document is out of sync
    with the Interactions Pane and should be recompiled! > 

Restarting DrJava, saving, clicking `Reset`, etc., would not clear the
problem.

In any event, at some point I noticed the Console tab was full of
messages like:

    Console
      Compiler is using classPath = '[/home/krb/Projects/Software/java,
    /home/apps/drjava/drjava-beta-20190813-220051.jar]';  bootClassPath
    = 'null' Fatal Error: Unable to find package java.lang in classpath
    or bootclasspath

At this point, I tried various things, but I focused on pointing DrJava
to an Oracle Java JDK I had installed a few days ago.  Everything I did
was in `Edit | Preferences ... | Resource Locations`, though I beat
around in there a while.  All of the settings were "blank" before I
started.  Anyway, I eventually had some success after I'd set:

    Web Browser
     /usr/lib64/firefox/firefox
    Web Browser Command
   
    Tools.jar Location
      /home/raid/apps/oracle/jdk-1.8.0_251/jre/lib/tools.jar
    Display All Compiler Version [ ]
    Extra Classpath
      /home/raid/apps/oracle/jdk1.8.0_251/jre/lib
      /home/raid/apps/oracle/jdk1.8.0_251/lib

> NOTE:  Your PATHs will NOT be the same as mine!  You need to use the
> actual paths on your system.  In my case I searched for "rt.jar" and
> "tools.jar" that were obviously in folders related to an installed
> JDK.

At this point I decided to try to figure out the minimum required to
get it working.  After a lot of fiddling around, I found it is
sufficient just to set `Preferences | Resource Locations | Tools.jar
Location`, but ***with with one MAJOR caveat.  You must BROWSE to the
file using that dialog.  YOU CANNOT JUST PASTE IN THE PATH!***  If you
just paste in the path, it can look like it is set correctly, but the
compiler will continue to not work.  This was how I got the oracle jdk
compiler to work.

Next, I set about to see if I could get OpenJDK to work.  I searched my
entire system for another `tools.jar` that belonged to OpenJDK, and did
not find one.  Then I realized I did not have the DEVEL OpenJDK package
installed (on Mageia Linux 7).

    java-1.8.0-openjdk-headless-1.8.0.252-1.b09.1.mga7
    java-1.8.0-openjdk-1.8.0.252-1.b09.1.mga7

I installed:

    java-1.8.0-openjdk-devel-1.8.0.252-1.b09.1.mga7

Now, even after resetting defaults, DrJava no longer says it is using
`JDK 8.0_222`, but rather `JDK
8.0-openjdk-1.8.0.252-1.b09.1.mga7.x86_64-OpenJDK`, and everything
works fine with NO customization to preferences!

I don't know where the heck `JDK 8.0_222` came from.  There's nothing
on my system with that version.  I rather suppose it is some internal
thing in DrJava.  I think the takeaways are:

* If DrJava says its using `JDK 8.0_222`, it probably is not going to
  work!
* Make sure you actually have a `tools.jar` installed if your system
  might split up the OpenJDK installation.
* Point `Tools.jar Location` to an existing `tools.jar` file where the
  JDK you are using is installed, and making sure to browse to it (not
  just paste in a path).