What is the difference between public,private,protected and default access modifiers in classes in java?

Question

if I do private static class Apple{},then the apple class cannot be accessed by the main java class??

Answer 1

https://docs.oracle.com/javase/tutorial/java/javaOO/accesscontrol.html

Answer 2

These access modiiers prevent other classes from using the data in any way they want. For example, you can make a variable private so that another class inheriting the other class can't just manually change the variable. So instead your main class that has the private variable can have a function to set the variable but it'll go through filtering before being set. This is just an example, you can't do much more..