Index

Now let's look at object type. This section is hot 🔥.

😊 Yang	😇 Sally	😔 Kofi
🙂 Jiao	🤭 Yawo	😀 Bob
😁 Mary	😃 Khawla	🤫 Zada

Recall our set of nine persons (objects).

Can we generalize all of these into one general object type?

Person
😊
firstName

Let's define a simple object type for Person and give it one property:

firstName -- The first name of the specific person instance/object

We also use the term variable for property.
The terms general and specific are used a lot in object coding.

Ball Type

Recall our collection of many balls (objects).

Can we generalize all of these into one general object type?

Let's define an object type for Ball and give it these properties:

r -- radius of ball
color -- color of ball

Note that for real ball objects, "r" and "color" will vary. They are variables. We'll learn more about these later.
We might also call this type "Sphere"

Rectangle Type

Recall our collection of many rectangles (objects).

Can we generalize all of these into one general object type?

Let's define an object type for Rectangle and give it these properties:

width -- width of rectangle
height -- height of rectangle

Note that for real rectangle objects, "width" and "height" will vary. They are variables. We'll learn more about these later.

Rectangle Type vs Rectangle Objects

Here is another perspective.

We have one "Rectangle type".

We have many rectangle objects.

Properties

In the examples above we used the term "property" to define things like "width" and "height" of a Rectangle type.

There are many different terms that we will use interchangeably with "property":

property
field
variable
instance variable
attribute

These terms tend to have relatively "loose" meanings in object coding. Therefore, do not worry about their strict meaning, but rather simply understand that they are used to help define object types like in our examples.

Object Type Summary

We generalize a collection of many similar objects into one general type (or class).

The word "general" is key in object thinking. 🔥

Summary Table:

Concept	Also Called	Count	Quick Description
Type	Class (Next Chapter)	One	A single definition (e.g. "Person")
Object	Instance	Zero to many	Actual person objects. For example: "Zada", "Yang", "Yawo", "Bob", ...
Property	Field, Varibable, or Attribute	Zero to many for a given type	Aspects of an object like "width" and "height" (e.g. for a Rectangle type)

You can define any object type (class) you like. Just a few examples here to give you an idea: Airplane, Baby, Bird, Car, City, College, CollegeApplication, Computer, Country, House, Lake, Person, Player, Rectangle, Road, Student, Team, Train, etc.

Another way to look at it is to think of a general type (class) is like a "blueprint" or "plan". We have one "blueprint" idea for say a bicycle that can be used to construct many actual bicycles. Some parts of the individual bikes may vary (e.g. color), but they all follow the pattern of the blueprint.

Object Type References

Introduction To Objects With Java

Chapter 301 - Object Types

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