11: Examining Object-Oriented Programming in .NET framework

Creation PDF 417 in .NET framework 11: Examining Object-Oriented Programming

In an object-oriented approach to making nachos, I would first identify the types of objects in the problem: chips, beans, cheese, and an oven Then I would begin the task of modeling these objects in software, without regard to the details of how they will be used in the final program While I am doing this, I m said to be working (and thinking) at the level of the basic objects I need to think about making a useful oven, but I don t have to think about the logical process of making nachos yet After all, the microwave designers didn t think about the specific problem of my making a snack Rather, they set about the problem of designing and building a useful microwave After the objects I need have been successfully coded and tested, I can ratchet up to the next level of abstraction I can start thinking at the nacho-making level, rather than the microwave-making level At this point, I can pretty much translate my son s instructions directly into C++ code

Critical to the concept of abstraction is that of classification If I were to ask my son, What s a microwave he would probably say, It s an oven that If I then asked, What s an oven he might reply, It s a kitchen appliance that (If I then asked, What s a kitchen appliance he would probably say, Why are you asking so many stupid questions ) The answers my son gave to my questions stem from his understanding of our particular microwave as an example of the type of things called microwave ovens In addition, my son sees microwave ovens as just a special type of oven, which itself is just a special type of kitchen appliance In object-oriented computerese, my microwave is an instance of the class microwave The class microwave is a subclass of the class oven, and the class oven is a subclass of the class kitchen appliances Humans classify Everything about our world is ordered into taxonomies We do this to reduce the number of things we have to remember Take, for exam ple, the first time you saw an SUV The advertisement probably called the SUV revolutionary, the likes of which have never been seen But you and I know that that just isn t so I like the looks of some SUVs (others need to go back to take another crack at it), but, hey, an SUV is a car As such, it shares all of (or at least most of) the properties of other cars It has a steering wheel, seats, a motor, brakes, and so on I bet I could even drive one without first reading the owner s manual

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I don t have to clutter my limited storage with all the things that an SUV has in common with other cars All I have to remember is an SUV is a car that and tack on those few things that are unique to an SUV (like the price tag) I can go further Cars are a subclass of wheeled vehicles along with other mem bers, such as trucks and pickups Maybe wheeled vehicles are a subclass of vehicles, which includes boats and planes And on and on and on

Why do we classify It sounds like a lot of trouble Besides, people have been using the functional approach for so long, why change now It may seem easier to design and build a microwave oven specifically for this one problem, rather than build a separate, more generic oven object Suppose, for example, that I want to build a microwave to cook nachos and nachos only I wouldn t need to put a front panel on it, other than a START button I always cook nachos the same amount of time, so I could dispense with all that DEFROST and TEMP COOK nonsense My nachos-only microwave needs to hold only one flat little plate Three cubic feet of space would be wasted on nachos For that matter, I can dispense with the concept of microwave oven alto gether All I really need is the guts of the oven Then, in the recipe, I put the instructions to make it work: Put nachos in the box Connect the red wire to the black wire Bring the radar tube up to about 3,000 volts Notice a slight hum Try not to stand too close if you intend to have children Stuff like that But the functional approach has some problems: Too complex I don t want the details of oven building mixed into the details of nacho building If I can t define the objects and pull them out of the morass of details to deal with separately, I must deal with all the complexities of the problem at the same time Not flexible Someday I may need to replace the microwave oven with some other type of oven I should be able to do so as long as its inter face is the same Without being clearly delineated and developed sepa rately, it becomes impossible to cleanly remove an object type and replace it with another Not reusable Ovens are used to make lots of different dishes I don t want to create a new oven every time I encounter a new recipe Having solved a problem once, it would be nice to be able to reuse the solution in future programs The remaining chapters in this Part demonstrate how object-oriented lan guage features address these problems

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