What is the purpose of inner class in Java?

The purpose of Java inner classes is:

1. Encapsulation: Inner classes can access the private members of the outer class, thus achieving encapsulation of the outer class and hiding implementation details.
2. Inheritance: Inner classes can inherit from other classes or implement interfaces, thereby achieving multiple inheritance.
3. Code organization: Inner classes can group related classes together, making the code clearer and easier to maintain.
4. Callback: Inner classes can be used as an implementation method for callback functions, simplifying code writing and management.
5. Anonymous class: Inner classes can define anonymous classes when needed, avoiding the creation of new class files.
6. Implementing Interfaces: Inner classes can implement an interface, allowing for multiple implementations of the interface.

Overall, inner classes provide a way to define another class within a class, increasing code flexibility and readability, while also offering some special functionalities and applications.