Re: [Switch()]From String to enum

Lew <>
Mon, 14 Jan 2008 21:03:54 -0500
Stefan Ram wrote:

  One might want to write:

switch( args[ 0 ])
{ case "alpha":
  System.out.println( "alpha" );
  case "gamma":
  System.out.println( "gamma" );
  break; }

By which you mean "one might want to" but is not allowed to, right?

BTW, you should improve your indentation. I suggest you follow either the Sun
convention followed by nearly everybody, or the variant that puts opening
braces on their own line, followed by everybody else.

  If it is known, that ?args[ 0 ]? always is either
  ?alpha? or ?gamma?:

switch( args[ 0 ].charAt( 0 ))
{ case 'a':
  System.out.println( "alpha" );
  case 'g':
  System.out.println( "gamma" );
  break; }

  One also sometimes can switch on a hash code of
  the string, or even a perfect hash code.

In the "normal" hash code technique (i.e., Object.hashCode()) one would need
an if block to distinguish values that hash to the same number. Of course, in
both types of hash code one needs to control the hash code value of the
String, which means writing a holder class with a custom hashCode() (or
perfect version), then abstracting the actual values out to compile-time
constants for readability, e.g., 'SET'. Of course, at this point one has
virtually re-invented 'enum', so one might as well use enum in the first place.

  Otherwise, a possible emulation is:

class Switch
{ final java.util.Map<String,Runnable> me;
  Switch( final Object ... args )
  { me = new java.util.HashMap<String,Runnable>();
    for( int i = 0; i < args.length; i += 2 )
    me.put(( String )args[ i ],( Runnable )args[ i + 1 ]); }
  void by( final String text ){ me.get( text ).run(); }}

public class Main
{ public static void main( final String[] args )
  { new Switch
    ( "alpha", new Runnable(){ public void run()
        { System.out.println( "alpha" ); }},
      "gamma", new Runnable(){ public void run()
        { System.out.println( "gamma" ); }}).
    by( args[ 0 ]); }}

That is remarkably hideous. And way overkill.


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