A Simple Explanation of OOP

Types

You already know how you can declare variables and assign values to them.

For example, you can declare a variable called x.

int x;

And you can assign the value 5 to the variable x .

x = 5;

You can also declare a variable called y.

String y;

And you can assign the value "hello world" to the variable y .

y = "hello world";

The values you assigned to these two variables were of different types.

The variable x was assigned a value of 5 , which is of type int.

The variable y was assigned a value of hello world , which is of type String.

Both of these types are defined in the Java language.

But the Java language has a way for you to define types as well.

You can define the structure of values of type Car by defining a class.

class Car {
    int mileage;
    String name;
}

You can then declare a variable of type Car .

Car mySedan;

You can then assign a value to the mySedan variable.

mySedan = new Car();

And that’s object-oriented programming (OOP) — creating classes that define a type of values.