First Class

Java is an OOP (Object Oriented Programming) language i,e Java has classes.

A class is a description of an object
An object contains data and methods (We can call it instructions)
An object is like a special purpose computer.
A class is like the specs of the object computer.

There are 3 kinds of classes:

(I) Main class: contains the main method i,e, the start instruction
(II) Utility class: general tools
(III) Data class: used and defined by programmer i,e, custom class

A data type is a collection of values and operations on those values. Example: A class

Primitive types in Java:

int:
values: 37, -4, 0
operations: +, -, *, /, %

double:
values: 37.0, 14.99, -3.2
operations: +, -, *, /

char:
values: 'a', '3', '\', '\\'

boolean:
values: true, false
operations: !, &&, ||

To create an object of a class use the class constructor.
Classes have descriptions of methods.
A description has the following form:

return-type name(input)
or
void name(input)

NOTE:

pricePerItem -> method
PricePerItem -> class

String class

An object of the String class is a list (or sequence) of characters. The positions are 0, 1, 2, 3...

Example: "house" where h is at position 0, o at position 1, etc.

Some methods are:

char charAt(int position);
int indexOf(char ch);
int indexOf(String s);
boolean contains(String s);
String substring(int first, int last);
String replace(s1, s2); //replaces instances of s1 by s2

End of class 1, if questions or would like to give feedback, please, comment.