Pop up java window

Look in your System Preferences : Users & Groups : Login Items, and remove anything in there. Otherwise, you have installed software that is using the System launch daemon to start up something that expects the Java SDK installed and not just the JRE (runtime).

I purposely do not install Java, but for this to occur automatically there may be a third-party preference (.plist) file in one of the following locations that is attempting to start an application that has a Java SDK (aka JDK) dependency:

1. /System/Library/LaunchDaemons
2. /System/Library/LaunchAgents
3. /Library/LaunchDaemons
4. /Library/LaunchAgents
5. ~/Library/LaunchAgents

Or you may be doing something with LibreOffice/OpenOffice macros that requires the Java compiler (javac).

If you use the LibreOffice spreadsheet feature you may need the JAVA runtime from Apple: Java for OS X 2017-001

Installing that should stop those popups.

Also, in the LibreOffice Preferences : Advanced, make certain that you have Use a Java runtime environment, and all Optional features on that panel unchecked. The Java Runtime environment is JRE, not JDK, but none-the-less, uncheck it anyway.

Then you need to Install Java JDK. :)

Do you have any Adobe software installed?