I'd like to ask you in detail about . in Java.

left side .right side

. is an operator to access the right-hand side (RHS) name that belongs to the left-hand side (LHS). The left side can have classes, variables, and objects. The right-hand side must have names such as type, method, and field belonging to the left-hand side.

This means that the name on the right-hand side exists on the left-hand side to help you access it.

If you think about it in Korean, you can think of it as 's.

class Person {
    public void hello() { System.out.println("hello"); }
}

If you want to call a method called hello() when there is a class called Person as above, you will write it as follows.

Person p = new Person();
p.hello();

At this time, p.hello(); is to call p's hello(). p is actually any object created by newPerson(), so it would mean calling hello() of the object pointed by the p variable.