Re: Using enums to avoid using switch/if

From:
Wojtek <nowhere@a.com>
Newsgroups:
comp.lang.java.programmer
Date:
Tue, 09 Jun 2009 08:01:34 -0700
Message-ID:
<mn.49e17d9647db84fe.70216@a.com>
Lew wrote :

aks_java wrote:

 public enum Operation {
        PLUS {


Please consider using narrower indentation, four spaces per level or less.

            double eval(double x, double y) {
                return x + y;
            }
        },
        MINUS {
            double eval(double x, double y) {
                return x - y;
            }
        },
        TIMES {
            double eval(double x, double y) {
                return x * y;
            }
        },
        DIVIDE {
            double eval(double x, double y) {
                return x / y;
            }
        };

        abstract double eval(double x, double y);
    }

But here's my problem: In my program I've strings ("+" , "-", "/", "="
etc) instead of enums. I need a mechanism to map string to enum.


  public enum Operation
  {
   PLUS( "+" )
   {
    double eval(double x, double y)
    {
      return x + y;
    }
   },

   MINUS( "-" )
   {
    double eval(double x, double y)
    {
      return x - y;
    }
   },

   TIMES( "*" )
   {
    double eval(double x, double y)
    {
      return x * y;
    }
   },

   DIVIDE( "/" )
   {
    double eval(double x, double y)
    {
      return x / y;
    }
   };

   private final String sym;
   Operation( String sym )
   {
     this.sym = sym;
   }

   abstract double eval(double x, double y);

   @Override public String toString()
   {
     return this.sym;
   }

   public static Operation fromString( String nym )
   {
     if ( nym == null )
     {
      return null;
     }
     for ( Operation op : Operation.values() )
     {
       if ( nym.equals( op.sym ))
       {
         return op;
       }
     }
     return null;
   }
  }


Don't return null. Throw an exception instead.

--
Wojtek :-)

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