Debian Squeeze for AMD64 comes with OpenJDK Java preinstalled and ready to run. If you, for whatever reason, need to install Sun Java, the Sources list has to be modified:

Edit /etc/apt/sources.list, add “non-free”:

deb http://ftp2.de.debian.org/debian squeeze main non-free

Update:

ron@ron:~$ apt-get update

Check for available Sun Java Packages:

ron@ron:~$ apt-cache search sun-java6

The result may look something like this:

sun-java6-bin - Sun Java(TM) Runtime Environment (JRE) 6 (architecture dependent files)
sun-java6-demo - Sun Java(TM) Development Kit (JDK) 6 demos and examples
sun-java6-doc - Sun JDK(TM) Documention -- integration installer
sun-java6-fonts - Lucida TrueType fonts (from the Sun JRE)
sun-java6-javadb - Java(TM) DB, Sun Microsystems' distribution of Apache Derby
sun-java6-jdk - Sun Java(TM) Development Kit (JDK) 6
sun-java6-jre - Sun Java(TM) Runtime Environment (JRE) 6 (architecture independent files)
sun-java6-plugin - The Java(TM) Plug-in, Java SE 6
sun-java6-source - Sun Java(TM) Development Kit (JDK) 6 source files

Now install what you need, minimum is sun-java6-bin:

ron@ron:~$ apt-get install sun-java6-bin sun-java6-javadb sun-java6-jdk sun-java6-plugin

In order to accept the License Agreement, navigate to the Accept field with TAB.

Make Sun Java the Java runtime of your choice:

ron@ron:~$ update-java-alternatives -s java-6-sun

Check, if Java could be properly installed:

ron@ron:~$ java -version

java version "1.6.0_22"
Java(TM) SE Runtime Environment (build 1.6.0_22-b04)
Java HotSpot(TM) 64-Bit Server VM (build 17.1-b03, mixed mode)

Set Environment Variable $JAVA_HOME

Edit file /etc/profile, add:

JAVA_HOME="/usr/lib/jvm/java-6-sun"
export JAVA_HOME

Done!