why we use classes in Java?

Answer 1

class meant for encapsulation & abstraction in Java.
That means your code is capsulated into a single unit called class. class helps programmer to permit the access of his/her code written in the class I.e abstraction.

Answer 2

Read about Object Oriented Programming and it will help make more sense. Java, C#, and most OOP language use classes to represent objects.

Answer 3

because of oop