If you want to get 10.1.2 JDeveloper running with JDK 1.5 you might get an error message such as:
Error: Hotspot VM not supported
Error: JDeveloper can't recognize the JDK version
Tha last error message is because of the first. To work around this you should edit the $JDEV_HOME/jdev/bin/jdev.conf -file and comment out the line that shows:
After this you should be able to start JDeveloper 10.1.2.
You might get some weird sticky startup screen showing in front of the initial questionnaire windows. After passing these (either try moving the windows or just pressing Enter) you should be fine with JDeveloper.