we’ve successfully developed a simple GUI interface, using only a few lines of code. The major factor which works here is the entire class structure is re-usable, and can be applied to build a lot of other different User Interfaces too. The reader can try out his own GUI applications using this model and code structure to get a real-world picture of the OPB model.- we’ve successfully developed a simple GUI interface, using only a few lines of code. The major factor which works here is the entire class structure is re-usable, and can be applied to build a lot of other different User Interfaces too. The reader can try out his own GUI applications using this model and code structure to get a real-world picture of the OPB model.