Incompatible Java Versions for WindowBuilder

Question

I Installed WindowBuilder on Eclipse to create a Graphic User Interface for a program. When I go to the 'Design' tab the following error appears:

Eclipse is running under 1.8, but this Java project has a 10 Java compliance level, so WindowBuilder will not be able to load classes from this project. Use a lower level of Java for the project, or run Eclipse using a newer Java version.

I currently have Installed Java 8 (Update 171), and Oxygen.3a (4.7.3a) (Eclipse Version). I had previously downloaded Java 10, but I read that there's a bug where WindowBuilder doesn't work on that version, and that it is recommened the Version 8, which is the one I downloaded and installed (after uninstalling Version 10). But the problem's still there.

What could I do to solve this? Thank you.

Nutgall

Can't you develop your project in Java 8? Your code should still compile in Java 10 with, at most, minor changes (unless you're depending on or doing some fancy stuff) – Sienna

@Sienna Yes of course I can, the problem here is that WindowBuider doesn't work. I don't know how to solve that problem :( I don't care about the version, the thing here is that the plugin doesn't work – Nutgall

"this Java project has a 10 Java compliance level" points to changing that value from the project's Properties dialog. – Capful

Answer 1

Just change the compliance level of the project from 10 to 1.8, rebuild and the Design tab should work:

1. To change the project's compliance level:

   • Select the project's node in Project Explorer, right-click and select Properties.
   • Select Java Compiler from the column on the left.
   • Uncheck Use Compliance from execution environment...
   • Select 1.8 from the drop list for Compiler compliance level. (Presumably its current value is 10.)
   • Click the Apply and Close button.
2. Rebuild the project using 1.8 compliance.
3. The Design tab should work fine now.

As a separate issue, since you have uninstalled Java 10 you should also remove it from your Installed JREs if you haven't done that already:

• Windows > Preferences > Java > Installed JREs
• Select the entry for JDK 10 and click the Remove button.
• If the JDK 10 entry was checked when you removed it you will be forced to check another JRE definition.
• Click the Apply and Close button.

Kailey

I did another project, added the windowbuilder application and now It works perfectly! Thank you so much. Thumbs up. – Nutgall

i did not have to uninstall any jre. All I did was to follow the first steps you listed for changing project compliance. thanks – Derringdo

@leeCoder You are right; uninstalling Java 10 is certainly not necessary to get everything working. But the OP mentioned that they had (unnecessarily) chosen to uninstall 10, so I just pointed out in my answer that it should also be removed from within Eclipse to complete the clean up process. – Kailey

Answer 2

WB 1.9.1 has solved the issue:

https://www.eclipse.org/windowbuilder/download.php

Bithia

I disagree. I still had this issue until l follow the accepted answer by skomisa – Derringdo

Answer 3

Just change the compliance level of the project from the current to 1.8, rebuild and the Design tab should work: It works for me

Immodest

How does this add anything to the answer posted by skomisa some time ago? – Cryometer