"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.
To be able to run Java programs, you can install OpenJDK from the repositories. This also installs a Java Development Kit.
# pacman -S openjdk6
To be able to run Java programs, you can install the Sun JRE from the repositories:
# pacman -S jre
You will need to log out and login again, or add /opt/java/jre/bin/ to $PATH to use the java bash command.
To create Java programs, you can install the Sun JDK from the repositories:
# pacman -S jdk
# source /etc/profile
BEA JRockit JIT JVM (+JDK)
Java sound with Pulseaudio
By default, Java and Pulseaudio don't get along very well with each other, but this is easy to fix using padsp.
(These paths are correct for Sun's Java, you will need to change the paths for OpenJDK)
First, rename the java binary to java.bin
# mv /opt/java/jre/bin/java /opt/java/jre/bin/java.bin
Then, create a new launcher script at /opt/java/jre/bin/java
#!/bin/sh padsp /opt/java/jre/bin/java.bin "$@"
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.