Nested Class

A nested class is a class defined within a class or method.

• A static nested class is associated with the containing class, not an instance.,
  • It can only access static fields/methods of the containing class.
• A non-static nested class (also known as an inner class)
  • Can access instance fields/methods

Local Class

A local class is a class defined within a function.

A local class can access the local variables of the enclosing method.

Given the following example:

class A {
  int x = 1;
 
  void f() {
    int y = 1;
 
    class B {
      void g() {
        x = y; // accessing x and y is OK.
      }
    }
 
    new B().g();
  }
}

B can access the x in A as well as y in f.

Variable Capture

We can access an instance of a local class outside of the function. To access the local variables in the enclosing method, the local class makes a copy of the local variables inside itself.

Effectively final

A local class can only access explicitly declared/implicit final variables. However, this can be circumvented by using reference types, which can be mutated.

Anonymous Class

Classes that are "single-use".

An anonymous class is a local class declared and instantiated in a single statement.
Similarly, it captures variables of the enclosing scope.