HI Satish,
I have not given the entire code. you have to make some declarations in the code to make ir functioning like the reference to ALV container, reference to ALV object etc.
Check any sample code for OOPs ALV. You will get a clear idea on how to go about it.
A simple program on ALV OOPS - Code Gallery - SCN Wiki
i_data type can be a table whose structure has just two fields- Order number and Message. This created to append all the messages that you want to display in your output.