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

Source: Internet
Author: User

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

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