Notes on Nested Classes

Use if class is only used with/by parent class.
Four kinds of nested classes, in order of preference.

1. static member classes
        * Access to all enclosing class static members, even private.
           Can acces other static peer member class fields.
        * Same visibility rule as regular static members.
        * Can be an interface
        * If member class does not require access to enclosing instance, always make member class static.  Save time and space on enclosing class construction.
        * Example, Map.Entry
        * Usage syntax: new Classname.StaticMemberClass()
2. nonstatic member classes
        * Access to all enclosing class static and instance members, even private.
        * Same visibility rule as regular instance members.
        * Cannot be interface
        * No static fields or methods, except for static final.
        * Can obtain explicit access to enclosing class instance members via
           Classname.this.instanceMember
     * Can obtain explicit access to the super class of the enclosing class via
           Classname.super.instanceMember
        * Usage syntax: classname.new NonStaticMemberClass() 
3. anonymous classes
        * Normally used as function objects
        * Good if class is short, used once, and right away.
        * No constructor but can use instance initializer
        * No static fields or methods, except for static final
4. local classes
        * Classes defined inside methods.
        * Can only use final fields of enclosing method.
        * Access to all enclosing class static and instance members, even private.
        * No static fields or methods, except for static final.