Install Java 7 on Debian 6

Get the Java (jdk) and extract jdk  into /usr/lib/jvm/

$ tar xvzf  jdk-7u5-linux-x64.tar.gz

$ update-alternatives --install /usr/bin/java java /usr/lib/jvm/jdk1.7.0_05/bin/java 1065

$ update-alternatives --install /usr/bin/javac javac /usr/lib/jvm/jdk1.7.0_05/bin/javac 1065

$ update-alternatives --config java

There are 4 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                      Priority   Status

------------------------------------------------------------

* 0            /usr/lib/jvm/jdk1.7.0_05/bin/java          1065      auto mode

  1            /usr/bin/gij-4.4                           1044      manual mode

  2            /usr/lib/jvm/java-6-openjdk/jre/bin/java   1061      manual mode

  3            /usr/lib/jvm/java-6-sun/jre/bin/java       63        manual mode

  4            /usr/lib/jvm/jdk1.7.0_05/bin/java          1065      manual mode

Finally, replace the symbolic link for mozilla plugin via

 ln -sf /usr/lib/jvm/jdk1.7.0_05/jre/lib/amd64/libnpjp2.so  /etc/alternatives/mozilla-javaplugin.so

Reference : http://alexander.holbreich.org/2011/11/java-7-on-debian/