How to upgrade from JDK 1.6 to 1.7 on ubuntu?

Its simple... Use the command 

sudo apt-get install openjdk-7-jre

This will install JDK 1.7 on your ubuntu box. But there is a catch.. if you still run java -version, it will tell you that it is still using JDK 1.6. 

So your system has actually been updated with JDK 1.7 but it is still not in use. There is a special script in ubuntu which allows you to check different versions present on the system and let's you choose the correct one you want to activate. 

Here is how you can update that: 

sudo update-alternatives --config java

This command will give you an output similar to below.. and asking you to choose which one you want to use.. 

There are 2 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
* 0            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      auto mode
  1            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      manual mode
  2            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1051      manual mode


Press enter to keep the current choice[*], or type selection number:

Simple.. Isn't it?