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• Enumeration (enum)


  A data type that contains a fixed set of constants
• Enums are good to use when you already know all possibilities of the values or instances of the class
• With enums, it is impossible to create an invalid enum value without introducing a compiler error
• Examples of when enumerations are useful

  • Compass directions
  • Months of the year
  • Cards in a deck
• Creating an enum


  1. Declare a type with the enum keyword

  2. Provide an identifier for the type

  3. List the enum constants
• Enum constants


  • The only allowed values for the enum type
• Enum methods


  • toString()
  • ordinal()
  • equals()
  • compareTo()
• Static enum methods


  • valueOf()
  • values()
• Enums can be declared in their own file or within a class, but not within a method
• Using enums in a switch statement

  • Displaying pizza prices based on size
• Type-safe


  Allows only appropriate behaviors
• Nested class


  A class created within another class
• Types of nested classes

  • Static member class
  • Non-static member class (inner class)
  • Local class
  • Anonymous class
• Reasons for nesting a class

  • The inner class is used only by the top-level class
  • Makes the connection between the classes easier to understand
  • Makes the code easier to maintain
• Example of a nested class

  • RealEstateListing class with a nested HouseData class
• Inner classes can access their top-level class's fields and methods, even if they are private
• Outer classes can access their inner class's members
• Nested classes are not frequently created, but they are seen in some built-in Java classes