如何将默认的Eclipse Oxygen编译器合规性级别从9更改为1.8，而不是将其恢复为9？

Question

When I open a workspace in Eclipse Oxygen , the default compiler compliance level is set to 9 . I change it in Preferences > Java > Compiler back to 1.8 and click Apply. It works, until I close Eclipse and reopen it and now it's back to 9 . How can I make the change stick?

Note: I know that /instance/org.eclipse.jdt.core/org.eclipse.jdt.core.compiler.compliance is set somewhere to 9, but I can't find out where that is.

Answer 1

I cannot replicate your problem of compliance changes not persisting across restarts, but you can manually set them rather than using Eclipse's GUI. To do that:

• Close Eclipse.

• Locate your preferences file. This is a text file containing many of settings you normally assign in Eclipse using Window > Preferences . The file will be in your workspace directory within the .metadata directory with the following name:

  .metadata.plugins\\org.eclipse.core.runtime.settings\\org.eclipse.jdt.core.prefs

• Open the file org.eclipse.jdt.core.prefs in a text editor and edit the following three lines:

org.eclipse.jdt.core.compiler.codegen.targetPlatform=9

org.eclipse.jdt.core.compiler.compliance=9

org.eclipse.jdt.core.compiler.source=9

• Replace the three instances of "9" with "1.8" for JDK 1.8 compliance (or "10" for JDK 10 compliance). Those three properties correspond to the three fields you see on the Compiler screen which specify a version, as shown below.
• Restart Eclipse and go to Preferences > Java > Compiler . The settings for the compiler should now all be set to 1.8:

This approach worked for me. However, even if this approach solves your problem, you could still raise a Bug Report with Eclipse since it should not be necessary to manually edit the preferences file.

Answer 2

My workspace settings were getting over-written by user-specific settings stored in ~/.eclipse/org.eclipse.oomph.setup/setups/user.setup . Specifically, that file included those leftover setup lines from a previous installation:

<setupTask
      xsi:type="setup:PreferenceTask"
      key="/instance/org.eclipse.jdt.core/org.eclipse.jdt.core.compiler.codegen.targetPlatform"
      value="9"/>
  <setupTask
      xsi:type="setup:PreferenceTask"
      key="/instance/org.eclipse.jdt.core/org.eclipse.jdt.core.compiler.compliance"
      value="9"/>
  <setupTask
      xsi:type="setup:PreferenceTask"
      key="/instance/org.eclipse.jdt.core/org.eclipse.jdt.core.compiler.source"
      value="9"/>
</setupTask>

Solution: Remove the lines above from ~/.eclipse/org.eclipse.oomph.setup/setups/user.setup .

Note: Thanks to @skomisa who helped me figure this out.