I have downloaded both Android 4.2 source code and Android kernel source code (common) separately by following the procedure mentioned in Android website. But I am not able to get the way how to start compiling both kernel code and source code on Ubuntu 12.04. I have also downloaded the Android Emulator.
Please mention the steps required to compile.
AOSP site contains Downloading and Building guide:
http://source.android.com/source/initializing.html
You should set up your local work environment to build the Android source files. You will need to use Linux (Ubuntu in yor case) or Mac OS. Building under Windows is not currently supported.
Note: The source download is approximately 8.5GB in size. You will need over 30GB free to complete a single build, and up to 100GB (or more) for a full set of builds.
Detailed instructions for Ubuntu and MacOS you can see on AOSP site. In general you will need:
Python 2.6 -- 2.7, which you can download from http://python.org.
GNU Make 3.81 -- 3.82, which you can download from http://gnu.org,
JDK 6 if you wish to build Gingerbread or newer; JDK 5 for Froyo or older. You can download both from http://java.sun.com.
Git 1.7 or newer. You can find it at http://git-scm.com.
Note: It is also possible to build Android in a virtual machine. If you are running Linux in a virtual machine, you will need at least 16GB of RAM/swap and 30GB or more of disk space in order to build the Android tree.
On XDA-developers you can see this Ubuntu-guide: http://forum.xda-developers.com/showthread.php?t=2114594
