Effective Java Item 30,32,33 fromString(), EnumSet and EnumMap

Correct way to implement enum's fromString. We should always use EnumSet and EnumMap because they are faster than HashMap.

 import java.util.*;  
 enum Operation {  
   PLUS("+"), MINUS("-"), TIMES("*"), DIVIDE("/");  
   private static final Map<String, Operation> stringToEnum = new HashMap<>();  
   static {  
     for (Operation op : values()){  
       stringToEnum.put(op.toString(), op);  
     }  
   }  
   private String symbol;  
   Operation(String symbol){  
     this.symbol = symbol;  
   }  
   public String toString(){  
     return symbol;  
   }  
   public static Operation fromString(String symbol){  
     return stringToEnum.get(symbol);  
   }  
 }  
 public class EnumSetMap {  
   public static void main(String[] args){  
     Set<Operation> enumSet = EnumSet.of(Operation.PLUS, Operation.MINUS);  
     Map<Operation, String> enumMap = new EnumMap<>(Operation.class);  
     System.out.println(Operation.fromString("+"));  
   }  
 }