Sitting at your desk in front of your workstation, you stare into space, trying to figure out how to write a new program feature. You know intuitively what must be done, what data and what objects come into play, but you have this underlying feeling that there is a more elegant and general way to write this program.
In fact, you probably don't write any code until you can build a picture in your mind of what the code does and how the pieces of the code interact. The more that you can picture this "organic whole," or gestalt, the more likely you are to feel comfortable that you have developed the best solution to the problem. If you don't grasp this whole right away, you may keep staring out the window for a time, even though the basic solution to the problem is quite obvious.
In one sense you feel that the more elegant solution will be more reusable and more maintainable, but even if you are the sole likely programmer, you feel reassured once you have designed a solution that is relatively elegant and that doesn't expose too much internal inelegancy.
One of the main reasons that computer science researchers began to recognize design patterns is to satisfy this need for elegant, but simple, reusable solutions. The term design patterns sound a bit formal to the uninitiated and can be somewhat off putting when you first encounter it. But, in fact, design patterns are just convenient ways of reusing object-oriented code between projects and between programmers. The idea behind design patterns is simple: write down and catalog common interactions between objects that programmers have frequently found useful.
One of the frequently cited patterns from early literature on programming frameworks is the Model-View-Controller framework for Smalltalk (Krasner and Pope 1988), which divided the user interface problem into three parts, as shown in Figure 1-1. The parts were referred to as a data model, which contains the computational parts of the program; the view, which presented the user interface; and the controller, which interacted between the user and the view.
Figure 1-1 The Model-View-Controller framework
Each of these aspects of the problem is a separate object, and each has its own rules for managing its data. Communication among the user, the GUI, and the data should be carefully controlled, and this separation of functions accomplished that very nicely. Three objects talking to each other using this restrained set of connections is an example of a powerful design pattern.
In other words, design patterns describe how objects communicate without become entangled in each other's data models and methods. Keeping this separation has always been an objective of good OO programming, and if you have been trying to keep objects minding their own business, you are probably using some of the common design patterns already.
0 comments:
Post a Comment