Re: Case expression must be constant expression

Owen Jacobson wrote:


Yes, actually I was trying to make a replacement for an Enum in JRE 1.3
when I stumbled accross this "Constant in case expression" problem.

What I made to mimic an enum is a class with static final members of
itself inside (see example code below). But in this case I can't use the
ordinal in a switch statement...

Phil

--SSCE-- (notice the missing C :-)

import java.util.HashMap;

public class Month{
   private final int ordinal;
   private static final HashMap correspondanceMap = new HashMap();

   private Month(int ordinal) {
     this.ordinal = ordinal;
     correspondanceMap.put(new Integer(ordinal), this);
   }

   public static final Month JANUARY = new Month(1);
   public static final Month FEBRUARY = new Month(2);
   public static final Month MARCH = new Month(3);
   public static final Month APRIL = new Month(4);

   public int getOrdinal(){
     return ordinal;
   }

   public static Month byOrdinal(int ordinal){
     return (Month)correspondanceMap.get(new Integer(ordinal));
   }

   public int hashCode() { return ordinal; }

   public boolean equals(Object h_type){
     if (!(h_type instanceof Month)) return false;
     if ( ((Month)h_type).getOrdinal() == getOrdinal()) return true;
     else return false;
   }

   public static void main(String[] args) {
     System.out.println("April's ordinal is: " + Month.APRIL.getOrdinal());

     Month m = Month.byOrdinal(2);
     if(m.equals(Month.FEBRUARY)){
       System.out.println("Both are equal.");
     }

     // switch doesn't work
     int choice = 3;
     switch(choice){
     case Month.JANUARY.getOrdinal():
       System.out.println("Do something for January");
     case Month.FEBRUARY.getOrdinal():
       System.out.println("Do something for February");
     case Month.MARCH.getOrdinal():
       System.out.println("Do something for March");
     case Month.APRIL.getOrdinal():
       System.out.println("Do something for April");
     default:
       System.out.println("None of those months");
     }
   }
}