Install Sun/Oracle Java JDK (Java Development Kit)/JRE (Java Runtime Environment) 6u21 on Fedora 14, Fedora 13, Fedora 12, CentOS 5.5, Red Hat (RHEL) 5.5 and Red Hat (RHEL) 6

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1. Download Sun/Oracle Java JDK or JRE RPMs

Download Sun/Oracle Java JDK or JRE from here (current version is JDK 6 Update 21) http://www.oracle.com/technetwork/java/javase/downloads/index.html.
Note: Select rpm.bin package (example jdk-6u21-linux-i586-rpm.bin, jre-6u21-linux-i586-rpm.bin, jdk-6u21-linux-x64-rpm.bin or jre-6u21-linux-x64-rpm.bin).

2. Change to root user.

sudo -i
## OR ##
su -

3a. Run Sun/Oracle Java JDK binary

chmod +x /path/to/file/jdk-6u21-linux-*-rpm.bin
/path/to/binary/jdk-6u21-linux-*-rpm.bin
 
## OR ##
 
sh /path/to/binary/jdk-6u21-linux-*-rpm.bin

Note: Use full file name (without asterix) if you have both i586 and x64 versions downloaded.

3b. Run Sun/Oracle Java JRE binary

chmod +x /path/to/file/jre-6u21-linux-*-rpm.bin
/path/to/binary/jre-6u21-linux-*-rpm.bin
 
## OR ##
 
sh /path/to/binary/jre-6u21-linux-*-rpm.bin

Note: Use full file name (without asterix) if you have both i586 and x64 versions downloaded.

4. Install Sun/Oracle java, Sun/Oracle javaws, Sun/Oracle libjavaplugin.so (for Firefox/Mozilla) and Sun/Oracle javac with alternatives –install command

alternatives --install /usr/bin/java java /usr/java/jdk1.6.0_21/jre/bin/java 20000
alternatives --install /usr/bin/javaws javaws /usr/java/jdk1.6.0_21/jre/bin/javaws 20000
 
## Java Browser (Mozilla) Plugin 32-bit ##
alternatives --install /usr/lib/mozilla/plugins/libjavaplugin.so libjavaplugin.so 

    /usr/java/jdk1.6.0_21/jre/lib/i386/libnpjp2.so 20000
 
## Java Browser (Mozilla) Plugin 64-bit ##
alternatives --install /usr/lib/mozilla/plugins/libjavaplugin.so libjavaplugin.so 

    /usr/java/jdk1.6.0_21/jre/lib/amd64/libnpjp2.so 20000
 
## Install javac only if you installed JDK (Java Development Kit) package ##
alternatives --install /usr/bin/javac javac /usr/java/jdk1.6.0_21/bin/javac 20000

5. Check current java, javac, javaws and libjavaplugin.so versions

java -version
java version "1.6.0_21"
Java(TM) SE Runtime Environment (build 1.6.0_21-b06)
Java HotSpot(TM) Server VM (build 17.0-b16, mixed mode)
 
javac -version
javac 1.6.0_21
 
javaws
Java(TM) Web Start 1.6.0_21
[...]

Note: Check libjavaplugin.so with restarting Mozilla Firefox 
and writing about:plugins on address bar.

6. Swap between OpenJDK and Sun/Oracle JDK 

versions

alternatives --config java   # or javac or javaws or libjavaplugin.so
There are 4 programs which provide 'java'.
 
  Selection    Command
-----------------------------------------------
   1           /usr/lib/jvm/jre-1.6.0-openjdk/bin/java
   2           /usr/lib/jvm/jre-1.5.0-gcj/bin/java
*  3           /usr/java/jdk1.6.0_18/jre/bin/java
 + 4           /usr/java/jdk1.6.0_21/jre/bin/java
 
Enter to keep the current selection[+], or 

type selection number:

Note: java with [+] is currently on use

Post-Installation Setup

Add JAVA_HOME environment variable to /etc/profile file or $HOME/.bash_profile file

## export JAVA_HOME
export JAVA_HOME="/usr/java/jdk1.6.0_21"