Improve IDE setup instructions based on problems encountered

The Java compiler compliance setting is completely separate
from the Installed JRE's setting and must be set as well to
have the platform working.

Change-Id: I1af2185293cc86c8a8960e56c1d7189ecc0fec2f

diff --git a/README.md b/README.md
index 3db0acbd12f1119983f6503f9bbf4a9a528eb6b6..7567cd62f707287c053ebce320840d724907d55b 100644 (file)
--- a/README.md
+++ b/README.md
@@ -46,6 +46,9 @@ You can also use newer JDKs but 11 as an LTS version is recommended, especially
    installation to the list and select the added JRE as the active JRE.
 3. Open IDE preference page **Java / Installed JREs / Execution Environments**
    and ensure that your selected JDK is selected in the *Compatible JREs* for `JavaSE-1.6` - `JavaSE-11`.
+4. **Important:** Ensure that IDE preference page **Java / Compiler** has *Compiler compliance level* set to **11**.
+   Otherwise the IDE will use the JDTs compiler to produce the binary classes with the designated compliance level
+   regardless of what JRE you've installed to use for running your programs from the IDE.
 
 #### Clone Repository into Eclipse
 
@@ -95,4 +98,4 @@ which should now succeed.
 #### Test
 
 Open [releng/org.simantics.desktop.rcp.product/simantics-desktop.product](releng/org.simantics.desktop.rcp.product/simantics-desktop.product)
-and press `Launch an Eclipse application in Debug mode`. The basic desktop product should start.
\ No newline at end of file
+and press `Launch an Eclipse application in Debug mode`. The basic desktop product should start.