Information Expert

Basically, put code in the same object with the data. This sounds simple, but I continually see "data only" and "code only" objects. That is the way procedural programming did things, and it is the natural result of focusing on the process while writing code. OO programming requires a certain level of design work before coding starts, and applying the Information Expert pattern is critical to that effort.

http://thinkingthroughjava.blogspot.com/2011/05/grasping-gang-of-four.html