Overview of enumerations for new features of Java 28-4 JDK5 and custom enumeration classes

Enumeration

Enumeration overview

is to list the value of the variable one by one, and the value of the variable is limited to the range of values enumerated. Example: only 7 days a week, only 12 months a year.

Recall a singleton design pattern: A singleton class is a class with only one instance

So many examples are a class with multiple instances, but not an infinite number of instances, but a finite number of instances. This can be an enumeration class.

The custom enumeration class.

　

First edition: Non-parametric construction

1  Public classDirection {2     //Create several instances3      Public Static FinalDirection FRONT =NewDirection ();4      Public Static FinalDirection BEHIND =NewDirection ();5      Public Static FinalDirection left =NewDirection ();6      Public Static FinalDirection right =NewDirection ();7 8     //constructs the private, the others cannot create indefinitely9     PrivateDirection () {Ten     } One}

Second Edition: with parametric construction

1  Public classDirection2 {2     //Create several instances3      Public Static FinalDirection2 FRONT =NewDirection2 ("front");4      Public Static FinalDirection2 BEHIND =NewDirection2 ("after");5      Public Static FinalDirection2 left =NewDirection2 ("left");6      Public Static FinalDirection2 right =NewDirection2 ("Right");7 8     //constructs the private, the others cannot create indefinitely9     //Private Direction2 () {Ten     // } One  A     //add member variables and remove parameterless constructs -     PrivateString name; -  the     PrivateDirection2 (String name) { -          This. Name =name; -     } -  +      PublicString GetName () { -         returnname; +     } A}

Third version: Constructed method and parametric structure

1  Public Abstract classDirection3 {2     //Create several instances3     4     //because objects cannot be instantiated in an abstract class, that is not the case5     //Public static final Direction3 FRONT = new Direction3 ("front");6     //However, you can use the anonymous internal method, as follows:7     //This is to rewrite the new Direction3 ("former") {} This subclass object to the abstract method: Show (), and give the Father Direction3 FRONT. 8      Public Static FinalDirection3 FRONT =NewDirection3 ("front") {9 @OverrideTen          Public voidShow () { OneSystem.out.println ("front"); A         } -  -     }; the      Public Static FinalDirection3 BEHIND =NewDirection3 ("after") { - @Override -          Public voidShow () { -System.out.println ("after"); +         } -  +     }; A      Public Static FinalDirection3 left =NewDirection3 ("left") { at @Override -          Public voidShow () { -System.out.println ("left"); -         } -  -     }; in      Public Static FinalDirection3 right =NewDirection3 ("Right") { - @Override to          Public voidShow () { +System.out.println ("Right"); -         } the  *     }; $ Panax Notoginseng     //constructs the private, the others cannot create indefinitely -     //Private Direction2 () { the     // } +  A     //add member variables and remove parameterless constructs the     PrivateString name; +  -     PrivateDirection3 (String name) { $          This. Name =name; $     } -  -      PublicString GetName () { the         returnname; -     }Wuyi  the     //Adding abstract methods -      Public Abstract voidShow (); Wu}

Finally, the test class:

1  Public classDirectiondemo {2      Public Static voidMain (string[] args) {3         4         //Print the first way5Direction d =Direction.front;6System.out.println (d);//Print out Address value7System.out.println ("------------------------------------");8         9         //Print the second wayTenDirection2 D2 =Direction2.front; OneSystem.out.println (D2);//Print out Address value ASystem.out.println (D2.getname ());//before -D2 =Direction2.right; - System.out.println (D2); the System.out.println (D2.getname ()); -System.out.println ("------------------------------------"); -          -         //print a third way +Direction3 D3 =Direction3.front; -SYSTEM.OUT.PRINTLN (D3);//Print out Address value +System.out.println (D3.getname ());//before A         //It is supposed that abstract classes cannot invoke methods, but this can be adjusted.  at         //because new Direction3 ("front") {} This subclass object overrides the abstract method: Show () method, and run look to the right, there is show () - d3.show (); -D3 =Direction3.left; - System.out.println (D3); - System.out.println (D3.getname ()); - d3.show (); in     } -}

Overview of enumerations for new features of Java 28-4 JDK5 and custom enumeration classes