How to explain an object?

Question

It\'s been years since I thought of this, but I am training some real juniors soon and need to explain what an object is to someone who doesn\'t know what it is.

B

Answer 1

I would try starting with actual code. Hopefully they're at least slightly familiar with some language. Write a simple program without using any classes or OO design at all, and then show how it can be made clearer or easier to maintain or whatever, if you redo it using classes.

A good example would probably be something where there are several functions that all use the same set of variables. For example (this is just the first example I could think of. You could probably think of much better ones -- hopefully something that doesn't seem too contrived and resembles something that you would actually write for a real-world project):

void printContactInfo(String name, String address, String phoneNumber) {
    System.out.println(name + " lives at " + address + " and his/her phone number is + "phoneNumber");
}

You write the code above, then at some point later, you decide that you'd also like to include the person's email address and username. Or you are dealing with two different people. You could easily end up with unwieldy functions that take several arguments, or have zillions of variables to keep track of. Or you could write a Person class, and you'd just call:

Person someguy = new Person("MatrixFrog", "123 Notareal Street", "555 5555");
someguy.printContactInfo();

Again, probably not the best example. And I do agree with mad-j that these little "car" and "person" examples aren't always great. But I think if you presented the example as a solution to an actual problem that comes up while writing code, it might be clearer.

Same thing with inheritance. The idea is based on the real-world understanding that "An X is a certain type of Y" but the reason we do it is to make code easier to read and write. I don't think I really understood inheritance until the first time I found myself writing two classes with a lot in common, and thinking, "Wait. These have a lot of the same properties. Maybe I should put their common properties into a superclass!"