switch case with '<='

[Adomini]

Dumb question, but I keep getting an error.

Error in Eclipse says "Invalid char constant" when I do the following:


case'==':

OR

case '<=':

The rest like case '<': are just fine. I have used " ", but those are for strings.

How can I get the error to go away?

[Ronin]

Hi Adomini,

Anything enclosed in single quotes is seen as a single char which is why '<' works ok. You cannot use '==' as this is an invalid use of the single quotes.

Regards.

[Adomini]

Right. But "" does not work either because those are set for Strings.

when I do two of the singular marks ( '' ) it does not work either. There has got to be a way to do this case-wise without resorting to if-else statements.

[Ronin]

Strings are permitted within switch statements in Java 7.
Can you show us exactly what you are attemting to code.

Regards.

[Adomini]

Sure!

switch (line.charAt(index))
{
case '+':
tok = TokenType.ADD_OP;
break;
case '<=':
tok = TokenType.LESSOREQUAL;
break;

** Ignore the tokenTypes - these are fine. Its just the case '<=' and such like it that cause the error.

[Ronin]

The switch is not going to work in the way you intend. The parameter used in your switch statement is a single char so even if this was a valid function '<=' will never match as this are two chars.

You will need to rethink your switch parameter or case statements.

Regards.

[jim829]

Why not use an enum type? Then you wouldn't need a switch statement. Here is a sample of what you might do.

enum TokenType {
   ADDOP("+"), LESSOREQUAL("<="), GREATEROREQUAL(">=");
   private String token;
   private static Map<String, TokenType> tokens = new HashMap<String, TokenType>();
   private TokenType(String token) {
      this.token = token;
   }
   static {
      for (TokenType t : values() ) {
         tokens.put(t.getToken(),t);
      }
   }
   
   public String getToken() {
      return token;
   }
   
   public static TokenType getValue(String token) {
      return tokens.get(token);
   }
   
}
public class enumTest {
   public static void main(String[] args) {
      
      String[] tokens = new String[]{ "+", "<=", ">="
      };
      
      for (TokenType t: TokenType.values()) {
         System.out.println(t.name() + "  " + t.getToken());
      }
      
      for (String t : tokens) {
         System.out.println(t + " maps to " + TokenType.getValue(t));
      }

   }

}

Enums are great for this type of thing. You can even use them as an entire class for a pretty indestructible singleton.

Regards,
Jim

[Adomini]

Jim,

I feel really bad if you just typed up that whole thing. I used some if -else logic in a couple of my "cases" so it flowed.

I looked on how to put this thread as solved.... but could not find it. Dude, I am so sorry.....

[jim829]

Absolutely no reason to apologize. I enjoy this stuff. Perhaps someone can use the construct.

Regards,
Jim

[JosAH]

I looked on how to put this thread as solved.... but could not find it. Dude, I am so sorry.....

I did it for you; you have to edit your OP in 'advanced mode' and add a prefix to your title.

kind regards,

Jos