For Redhat Linux installation, both EL and Fedora, GCJ is installed as the default JDK. But GCJ can not catch up with Sun JDK. So I have to install Sun manually again and again.

Install Sun JDK itself is pretty easy, just go to http://java.sun.com to download either an RPM BIN package or a BIN package, run it, then done.

What's really need to google and remember is that, switch from GCJ to Sun JDK.

# /usr/sbin/alternatives --install /usr/bin/java java /usr/java/jdk1.6.0_02/bin/java 2

# /usr/sbin/alternatives --config java

There are 2 programs which provide 'java'.

  Selection    Command
-----------------------------------------------
*+ 1           /usr/lib/jvm/jre-1.4.2-gcj/bin/java
   2           /usr/java/jdk1.6.0_02/bin/java

Enter to keep the current selection[+], or type selection number: 2

# java -version

java version "1.6.0_02"
Java(TM) SE Runtime Environment (build 1.6.0_02-b05)
Java HotSpot(TM) Client VM (build 1.6.0_02-b05, mixed mode, sharing)