Java Enum example

import java.util.EnumSet;

import java.util.HashMap;
import java.util.Map;

public class EnumExample{
 public static void main(String args[]){
  // To Get the 'Day' by Abbreviation: 
  System.out.println("1 ="+Day.get("Su"));
  System.out.println("2 ="+Day.findByAbbr("Su"));
  // To get 'Day' name in String:
  System.out.println("3 ="+Day.valueOf("SUNDAY").toString());
  
  // To Get the Abbreviation by 'Day': 
  System.out.println("4 ="+Day.SUNDAY.getAbbreviation());
  System.out.println("5 ="+Day.valueOf("SUNDAY").getAbbreviation());  
 }
}

/**
 * Usage: 
 * 1. To Get the 'Day' by Abbreviation: Day.get("Su"))<br/>
 * 2. To Get the Abbreviation by 'Day': <br/>
 *    Day.SUNDAY.getAbbreviation();<br/>
 *        OR <br/>
 *    Day.valueOf("SUNDAY").getAbbreviation(); <br/>
 * 3. To get 'Day' name in String:<br/>
 *    Day.valueOf("SUNDAY").toString();
 */
 enum Day {
 //Enum types
 SUNDAY("Su"), MONDAY("Mo"), TUESDAY("Tu"), WEDNESDAY("We"), THURSDAY("Th"), FRIDAY("Fr"), SATURDAY("Sa");

 //internal state
 private final String abbreviation;

 // Reverse-lookup map for getting a day from an abbreviation
 private static final Map<String, Day> lookup_0 = new HashMap<String, Day>();
 
 
 
 // Populate the lookup table on loading time
 static {
  for (Day d : Day.values()) {
   lookup_0.put(d.getAbbreviation(), d);
  }
 }
 //Alternative way populating lookup table
 /*
 static {
  for (Day d : EnumSet.allOf(Day.class)) {
   lookup_0.put(d.getAbbreviation(), d);
  }
 }*/

 //Constructor
 private Day(final String abbreviation) {
  this.abbreviation = abbreviation;
 }

 public String getAbbreviation() {
  return abbreviation;
 }
 
 // This method can be used for reverse lookup purpose
 public static Day get(String abbreviation) {
  return (Day)lookup_0.get(abbreviation);
 }
 
 public static Day findByAbbr(String abbreviation){
     for(Day d : values()){
         if( d.abbreviation.equals(abbreviation)){
             return d;
         }
     }
     return null;
 }
}