"Java is a programming language originally developed by Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture." 
There are two Java Virtual Machines in the Arch repos that can be installed on your system — the OpenJDK open source implementation and Sun's closed source implementation. Arch recommends OpenJDK.. Additional Java implementations are available via the AUR.
To be able to run Java programs, you can install OpenJDK from the repositories. This also installs a Java Development Kit.
# pacman -Syu openjdk6
You will likely need the icedtea-web for Java functionality in Firefox as suggested in this thread: https://bbs.archlinux.org/viewtopic.php?pid=895343
# pacman -Syu icedtea-web
To be able to run Java programs, you can install the Oracle JRE from the repositories:
# pacman -S jre
You will need to log out and login again, or add /opt/java/jre/bin/ to $PATH to use the java bash command.
To create Java programs, you can install the Oracle JDK from the repositories:
# pacman -S jdk
# source /etc/profile
Kaffe is another clean-room implementation of a Java VM without official endorsement from Sun/Oracle. A git package of Kaffe can be found in the AUR. The Kaffe VM is redistributed according to the GPL license.
BEA JRockit JIT JVM (+JDK)
VMkit LLVM-based JIT VM
VMkit is an LLVM-based framework for JIT virtual machines. J3 is a JVM running on VMkit. A broken build for VMkit can be found in the AUR. J3 depends on the GNU classpath libraries, but may also work with the Apache class path libraries.
Java sound with Pulseaudio
By default, Java and Pulseaudio don't get along very well with each other, but this is easy to fix using padsp.
(These paths are correct for Sun's Java, you will need to change the paths for OpenJDK)
First, rename the java binary to java.bin
# mv /opt/java/jre/bin/java /opt/java/jre/bin/java.bin
Then, create a new launcher script at /opt/java/jre/bin/java
#!/bin/sh padsp /opt/java/jre/bin/java.bin "$@"
Finally, make the launcher script executable
# chmod +x /opt/java/jre/bin/java
You will need to redo this process on each update of Java.
You can also try replacing padsp with aoss, which can also fix it under standard ALSA as well as in Pulse, do what works best. I must warn everyone that these hacks sometimes work perfect, but are sometimes very unstable as well.
Due to the fact that the JDBC-drivers often use the port in the URL to establish a connection to the database, it is considered "remote" (i.e., MySQL does not listen to the port as per its default settings) despite the fact that they are possibly running on the same host, Thus, to use JDBC and MySQL, you need to edit /etc/mysql/my.cnf and comment out the line looking like this: