What are the differences between Java and Kotlin inner/local/anonymous classes?

Question

What are the name equivalents and main differences between Java and Kotlin nested/inner/local classes?

Answer 1

These are the name equivalents:

| Kotlin            | Java                                      |
|-------------------|-------------------------------------------|
| Inner Classes     | Non-Static Nested Classes / Inner Classes |
| Nested Classes    | Static Nested Classes                     |
| Local Classes     | Local Classes                             |
| Anonymous Objects | Anonymous Classes                         |

This is a quick overview of differences:

• In both cases, we can group multiple classes in the same file. However, in Kotlin we can have multiple top-level classes in the same .kt file, in Java we can have many classes per compilation unit but only one can be public.
• Kotlin anonymous objects have support to implement multiple interfaces.
• Java anonymous classes are limited to implement only one abstract class or interface.
• In Kotlin we can mutate a local variable from a closure; because of that the Java concept of effectively final doesn't apply to Kotlin.

• In Kotlin inner classes to reference the instance of the outer class, we need to use the qualifier this expression.

  Some examples can be found over on this tutorial.