to install java I have always used the classic way from the terminal. I would like to install java manually. I placed the folder of the JDK on the desk and I set environment
In addition to flup's answer you might also want to run the following to set JAVA_HOME and PATH:
sudo apt-get install oracle-java7-set-default
More information at: http://www.ubuntuupdates.org/package/webupd8_java/precise/main/base/oracle-java7-set-default