Nested Classes

A class can contain other types within the class body, such as other classes, interfaces, enums, and records

Type	Description
static nested class	declared in class body. Much like a static field, access to this class is through the Class name identifier
instance or inner class	declared in class body. This type of class can only be accessed through an instance of the outer class
local class	declared within a method body
anonymous class	unnamed class, declared and instantiated in same statement.

As of JDK16, all four types of nested classes can have static members of any type, including static methods

InnerClass innerClass = new OutherClass.InnerClass();

OuterClass outerClass = new OuterClass();
OuterClass.InnerClass innerClass = outerClass.new InnerClass();

They don't have access modifiers
Can access local variables and method arguments, that are final or effectively final

When we create an instance of a local class, referenced variables used in the class, from the enclosing code, are ' captured'
This means a copy is made of them, and the copy is stored with the instance
This is done because the instance is stored in a different memory area, then the local variables in the method
For this reason, if a local class uses local variables, or method arguments, from the enclosing code, these must be final or effectively final

Local variable or a method argument are effectively final, if a value is assigned to them, and then never changed after that

var comparator = new Comparator<Employee>() { };

On the place of Comparator can be the super class of the anonymous class, or the interface this anonymous class will implement

Nested Classes​