java - What are the purposes of inner classes

Question

I am reviewing the concept of inner classes in java. so far from what I've understood and applied java inner classes has a link or access to the methods and fields of its outer/ enclosing class.

My Question:

1. When should create or define an inner class?
2. are inner classes considered to be called as "Helper classes" ?
3. What are the indicators for you to make an inner class and what's their other purpose?

Answer 1

Inner classes are best for the purpose of logically grouping classes that are used in one-place. For example, if you want to create class which is used by ONLY enclosing class, then it doesn't make sense to create a separate file for that. Instead you can add it as "inner class"

As per java tutorial:

Compelling reasons for using nested classes include the following:

• It is a way of logically grouping classes that are only used in one place.
• It increases encapsulation.
• It can lead to more readable and maintainable code.