Java enumeration (enum) detailed 7 common usage _java

JDK1.5 introduces a new type--enumeration. In Java it is a "small" function, but to my development has brought "big" convenience.

Usage One: Constants

Before JDK1.5, we defined constants as: public static fianl ... Now that you have enumerations, you can group related constants into an enumeration type, and enumerations provide more methods than constants.

 public enum Color { 
  RED, GREEN, BLANK, Yellow 
 

Usage Two: Switch

The switch statement before JDK1.6 only supports the Int,char,enum type, and using enumerations makes our code more readable.

 Enum Signal { 
   GREEN, yellow, RED 
 } public 
 class TrafficLight { 
   Signal color = signalred; 
   public void Change () { 
     switch (color) {case 
     RED: 
       color = signalgreen; 
       break; 
     Case YELLOW: 
       color = signalred; 
       break; 
     Case GREEN: 
       color = signalyellow; 
       break; 
     } 
   } 
 

Usage Three: Add a new method to the enumeration

If you intend to customize your own method, you must add a semicolon at the end of the sequence of enum instances. and Java requirements must first define an instance of an enum.

 The public enum Color {red 
   ("Red", 1), Green ("green", 2), BLANK ("White", 3), Yello ("Yellow", 4); 
   Member variable 
   private String name; 
   private int index; 
   Construction Method 
   Private Color (String name, int index) { 
     thisname = name; 
     Thisindex = index; 
   } 
   Normal method public 
   static String getName (int index) {for 
     (Color c:colorvalues ()) { 
       if (cgetindex () = = index) {return 
         cname; 
       } 
     } 
     return null; 
   } 
   Get Set method public 
   String GetName () {return 
     name; 
   } 
   public void SetName (String name) { 
     thisname = name; 
   } 
   public int GetIndex () {return 
     index; 
   } 
   public void Setindex (int index) { 
     thisindex = index; 
   } 
 

Usage Four: Methods of overriding enumerations

An example of a ToString () method overlay is given below.

 The public enum Color {red 
   ("Red", 1), Green ("green", 2), BLANK ("White", 3), Yello ("Yellow", 4); 
   Member variable 
   private String name; 
   private int index; 
   Construction Method 
   Private Color (String name, int index) { 
     thisname = name; 
     Thisindex = index; 
   } 
   Override method 
   @Override public 
   String toString () {return 
     thisindex+ "_" +thisname; 
   } 
 

Usage Five: Implement Interface

All enumerations inherit from the Java.lang.Enum class. Because Java does not support multiple inheritance, enumeration objects can no longer inherit other classes.

 Public interface Behaviour { 
   void print (); 
   String getInfo (); 
 } 
 Public enum Color implements behaviour{red 
   ("Red", 1), Green ("green", 2), BLANK ("White", 3), Yello ("Yellow", 4); 
   Member variable 
   private String name; 
   private int index; 
   Construction Method 
   Private Color (String name, int index) { 
     thisname = name; 
     Thisindex = index; 
   } 
 Interface method 
   @Override public 
   String GetInfo () {return 
     thisname; 
   } 
   Interface method 
   @Override public 
   void print () { 
     systemoutprintln (thisindex+ ":" +thisname); 
   } 
 

Usage Six: Organize enumerations using interfaces

Public interface Food { 
   enum Coffee implements food{ 
     Black_coffee,decaf_coffee,latte,cappuccino 
   } 
   enum Dessert implements food{ 
     FRUIT, CAKE, GELATO 
   } 
 

Usage Seven: About the use of enumeration collections

Java.util.EnumSet and Java.util.EnumMap are two enumerated collections. Enumset guarantees that the elements in the collection are not duplicates; The key in Enummap is the enum type, and value can be any type. The use of this two collection is not here to repeat, you can refer to the JDK documentation.

For the implementation details and principles of enumerations, please refer to:

Reference: "Thinkinginjava" fourth edition http://www.jb51.net/books/75540.html

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