OK, after I did the manual updating as was explained in the last post, I was unable to run my applet. The Java Console throws java.lang.ExceptionInInitializerError error. I did not know what went wrong.
After googling, I arrived at the following information.
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Run sudo update-java-alternatives -l to see the current configuration and possibilities.
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Run sudo update-java-alternatives -s XXXX to set the XXX java version as default. For Sun Java 6 this would be sudo update-java-alternatives -s java-6-sun
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Run java -version to ensure that the correct version is being called.
I ran the command, and the following was the result on my console:
java-6.19-sun 60 /usr/lib/jvm/java-6.19-sun
java-6-sun 63 /usr/lib/jvm/java-6-sun
java-gcj 1042 /usr/lib/jvm/java-gcj
java -version shows:
Java(TM) SE Runtime Environment (build 1.6.0_19-b04)
Java HotSpot(TM) Server VM (build 16.2-b04, mixed mode)

So, my manual installation works. But why does running applets throw the above error? So I decided to revert to java-6-sun. And the exception does not show again. What went wrong?