What's the best way to define the words "class" and "object" to someone who hasn't used them?

Question

My neighbor is taking "Intro to Java", and asked me to help explain a few of the first-day concepts. I realized that since I do this everyday, I don't have the beginner's mind, and it's hard to relate some of this stuff from scratch.

The one that's actually not trivial for me to explain is "what the heck is a class?"

Best I have so far:

• A variable holds some kind of data; one variable might be a first name, another variable might be your weight in pounds.

• A method is a function, it does stuff, and can do stuff with those variables. A method might display your name on screen, or tell you how much weight you should lose to have a good BMI ratio.

• An object holds both variables and methods; one object might represent you, a second object might represent me.

• A class is kind of the blueprint or template that describes the methods and variables that will be in each object. An object is an instantiated (instance of a) class; an object is something, while the class is simply the plans to make that something.

Continuing the example, we have a Person object, which is instantiated to hold Alice's data, and another Person object instantiated to hold Bob's data, and another for Carol, and so on.

How do I tune this example to make more sense, and/or what's a better approach? The word "instantiated" feels too heavy at this point.

(I think this is a useful question, but is obviously subjective; marked as community wiki.)

Solution 1

A class and some class instances:

(public domain image hosted by wikipedia)

Solution 2

Class : Object :: Blueprint : Building

Solution 3

"Car" is a class. My car, sitting in my driveway, is an instance (object).

Solution 4

One of the examples I use during my java courses is the Human class.

Everyone reading this is a Human (I least I hope so !), we all have our differences our resemblances but at the end we're all Human (After all).

Each Human (known as an instance or object) has specific characteristics such as the eyes color or the voice which are the fields (you called that variables, but the right name would be fields). But the values are different from an Human instance to another.

There is also a common knowledge, shared with the humanity, principles like the "Pythagorean theorem". This knowledge is common, it can be interpreted as a static field (I know it's an exaggeration) which means that this knowledge is not only contained in one human but in the humanity.

Every Human can do things such as walking, speaking etc. this is known as method, walking is the same for everyone, but when I walk, not everyone walk. The act of walking only affects the Human instance which does this, but still it's defined by the Human class

---

If you want to get deeper in OOP, Teaching OOP to non-programmers

Solution 5

An object is a thing. A class is a category of things.

"Person" is a class; you are an object, an instance of the Person class. Also, the word "you" can be thought of as a variable, since it refers to a Person, but not always the same Person.

View more solutions