I just had this exact problem with a fresh 11.04, setting up the Sun JDK was a doozie, and even then my CPU was spiking over 100% usage, whoa! I could hear the clock in my headphones
Here where my steps to solve it:
- Go to synaptic, enable the Canonical Partners repos (the two unchecked boxes)
completely remove the open jdk and jre.
- You should be prompted to mark the Sun JDK/JRE for install
- Install
java -version in a terminal you should get: Java(TM) SE Runtime Environment instead of the OpenJDK
- Try to fire up minecraft with
java -Xmx1024M -Xms512M -cp minecraft.jar net.minecraft.LauncherFrame
- At this point I was noticing the insane CPU usage when adding multiplayer servers (weird). On the main menu in options -> Video Settings change performance to Power Saver
I was stunned that this worked. I remember my old dell laptop had a CPU clock issue where I could hear the high freq in my headphones, the solution was to underclock the processor to get rid of the noise. Pretty cool, it's like underclocking the JVM or telling it to be more sparring with the CPU (which in this case solved made everything run smoothly)
Hope this helps someone