Java Basics---Enumeration

Before JDK1.5, Java can have two ways of defining new types: Classes and interfaces, and for most object-oriented programming, these two seem sufficient, but in some special cases it is inappropriate. For example, to define a color class, it can only have red,green,blue three, other values are errors, and an enumeration type is introduced after JDK1.5.

Enumeration is actually a type, similar to int, Char, which is the limit input when defining variables, you can only assign the values specified in enum.

public enum color{    Red,green,blue;    Defines the type of three enumerations};

There are three values in the enumeration, which can only be taken from these three items at a later time.

public class getenumcontent{public    static void Main (String args[]) {        Color c = color.blue;        Remove the blue        System.out.println (c);    }};

Can be used directly on the switch statement

public class switchprintenum{public  static void Main (String args[]) {for    (Color c:color.values ()) {// Output the entire contents of the enumeration      print (c);}  }  public static void print (color color) {    switch (color) {case      red:{        System.out.println ("Red Color");        break;      }      Case green:{        System.out.println ("green color");        break;      }      Case blue:{        System.out.println ("Blue Color");        break;      }      default:{        System.out.println ("Unknown Color");        Break;}}}  ;

You can define an enumeration by using the Enum keyword, or you can define a EUNM class

How to enumerate classes:

The enumeration already implements the comparable interface, so the content in the enumeration can be sorted.

Case One

Import java.util.iterator;import java.util.Set; import java.util.TreeSet; enum color{  Red,green,blue;} public class comparableenum{public  static void Main (String args[]) {    set<color> t = new treeset<color& gt; ();//set Type    t.add (color.green);//Add Green    t.add (color.red);//Add Red    t.add (Color.Blue);//Add Blue    Iterator<color> iter = T.iterator ();    while (Iter.hasnext ()) {      System.out.print (Iter.next () + ",");}}  };

Case listing Two

Using Enummap

Import java.util.EnumMap; import java.util.Map; enum color{  RED, GREEN, BLUE;} public class enummapdemo{public  static void Main (String args[]) {    map<color,string> desc = null;//define Map Object , specifying the type    desc = new Enummap<color,string> (color.class);//Instantiate Enummap object    desc.put (color.red, "Red");    Desc.put (Color.green, "green");    Desc.put (Color.Blue, "Blue");    System.out.println ("====== Output All content ======");    For (Color c:color.values ()) {      System.out.println (c.name () + "-" + Desc.get (c));    }    System.out.println ("====== output all key value ======");    For (Color C:desc.keyset ()) {      System.out.print (c.name () + ",");    }    System.out.println ();    System.out.println ("====== Output All content ======");    For (String s:desc.values ()) {      System.out.print (S + ",");}}}  ;

Case listing Three

Using Enumset

Import Java.util.EnumSet; enum color{  RED, GREEN, BLUE;} public class enumsetdemo{public  static void Main (String args[]) {    enumset<color> esold = null;//declaration of a enums Et object    enumset<color> esnew = null;    System.out.println ("======== enumset.copyof (Color.class) =====");    Esold = enumset.noneof (Color.class);//Set all types of enumerations into Enumset objects    Esold.add (color.red);//Add Content    Esold.add ( Color.green);//add content    esnew = enumset.copyof (esold);//Copy from existing set    print (esnew);  }  public static void print (Enumset<color> temp) {//Dedicated output action    for (Color c:temp) {///  loop output Enumset contents      System.out.print (c + ",");    }    System.out.println ();  }};

• This article is from: Linux Learning Tutorial Network

Java Basics---Enumeration