Incompatible Java Versions for WindowBuilder

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.

Answer

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.