Java Preferences won't start

[Anthony Petrov]

Hello,

My ls -l /Library/Java/JavaVirtualMachines/ looks like this:

total 0
drwxr-xr-x  3 root  wheel  102 Mar 28  2012 1.6.0_31-b04-413.jdk
drwxr-xr-x  3 root  wheel  102 Aug 24  2012 jdk1.7.0_06.jdk
drwxr-xr-x  3 root  wheel  102 Sep 18  2012 jdk1.7.0_10.jdk
drwxr-xr-x  3 root  wheel  102 May 17 15:51 jdk1.8.0.jdk

All the JDKs are usable when I run commands specifying their full path 
names. Also, the "default" jdk is the 7u10 one, so that running 'java 
-version' in the command line will say "1.7.0_10". The 1.8 is b90 
installed just now.

However, when I'm trying to start Java Preferences in order to select 
the default JDK for the command-line use, I get a small dialog box with 
an error saying:

Cannot launch "Java Preferences"
No compatible version of Java 1.5+ is available.

After I click Quit, the console output is as follows:

[JavaAppLauncher] Requested [1.5+], launching in [(null)] instead.
[JavaAppLauncher Error] unable to find a version of Java to launch

I tried searching this on the Internet but didn't find anything useful.

I don't even want to run this GUI tool actually. Is there a way to 
switch the default JDK from command line? (Yes, I know I can modify my 
PATH and JAVA_HOME, but I actually want to do the same thing that the 
Java Preferences tool does).

Any tips?

--
best regards,
Anthony