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Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA")

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On Monday, August 10, 2015 at 9:18:08 AM UTC-4, Eric Sosman wrote:
>      Besides, what advantage would switch on a boolean have, when
> compared to an if or if/else?
> 
> > then you could evaluate Strings in the case conditions by comparing your String to other Strings looking for the first case that evaluates to true.
> 
>      That can't work (unless I've completely misunderstood what you're
> saying).  The switch statement is not an if ladder.
> 
> > [...] The switch documentation states the switch value may now be a String starting with Java 7, int and enum also work.
> 
>      Section 14.11 of the JLS requires that the expression in switch
> must be char, byte, short, int, Character, Byte, Short, Integer,
> String, or an enum type.
> 
> > Eclipse also flags an error if a case value is not a constant,
> 
>      Evidence that Eclipse has read JLS section 14.11.
> 
>      By the way, is anyone else horrified at the bytecode generated for
> a switch on a String value?  It produces what amounts to *two* switch
> constructs *and* a set of if ladders (short ones with luck, but ...).
> Roughly speaking,
> 
> 	switch (theString) {
> 	case "Foo": fooStuff(); break;
> 	case "Bar": barStuff(); break;
> 	case "Baz": bazStuff(); break;
> 	}
> 
> turns into something like
> 
> 	int _case = 0;
> 	switch (theString.hashCode()) {
> 	case 70822: if ("Foo".equals(theString)) _case = 1; break;
> 	case 66547: if ("Bar".equals(theString)) _case = 2; break;
> 	case 66555: if ("Baz".equals(theString)) _case = 3; break;
> 	}
> 	switch (_case) {
> 	case 1: fooStuff(); break;
> 	case 2: barStuff(); break;
> 	case 3: bazStuff(); break;
> 	}
> 
> String-switching is a convenience, sometimes, but it's a costly one.

String switch may be ugly behind the scenes but makes the most readable code where the value you're checking is already a String.  int switch may be easier but if you start with a String you have to convert it.
        switch (theString) { 
        case "Foo": fooStuff(); break; 
        case "Bar": barStuff(); break; 
        case "Baz": bazStuff(); break; 
        } 
This construct is easily readable and allows fall-through.  If you wanted to do the same thing and say that all Foo are also Bar you could take out the break.
        switch (theString) { 
        case "Foo": fooStuff();
        case "Bar": barStuff(); break; 
        case "Baz": bazStuff(); break; 
        } 
Alternatives?
1) Write an if statement (values must be mutually exclusive?):
  if (theString.equals("Foo")) {
     fooStuff();
  } else {
  if (theString.equals("Bar")) {
     barStufF();
  } else {
  if (theString.equals("Baz")) {
     bazStuff();
  }
2) Write an int switch based on the if statement?
  final int stringMatch;
  if (theString.equals("Foo")) {
     stringMatch = 1;
  } else {
  if (theString.equals("Bar")) {
     stringMatch = 2;
  } else {
     stringMatch = 3;
  }
        switch (stringMatch) { 
        case 1: fooStuff(); break; 
        case 2: barStuff(); break; 
        case 3: bazStuff(); break; 
        }
With a boolean switch, if a case allows a variable, you could do what the OP suggests:
  switch (true) {
  case theString.equals("Foo"): fooStuff(); break;
  case theString.equals("Bar"): barStuff(); break; 
  case theString.equals("Baz"): bazStuff(); break; 
  } 
With this construct you could test anything from String matching to object methods which return boolean.

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PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") srcommunicationsvja@gmail.com - 2015-08-08 06:53 -0700
  Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-08-08 10:39 -0400
  Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eternal Hope <laughingspam99@gmail.com> - 2015-08-09 08:53 +0100
    Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") e.d.programmer@gmail.com - 2015-08-10 05:36 -0700
      Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-08-10 09:17 -0400
        Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") e.d.programmer@gmail.com - 2015-08-10 07:56 -0700
          Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-08-10 11:50 -0400
        Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Arne Vajhøj <arne@vajhoej.dk> - 2015-08-12 20:51 -0400
          Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eric Sosman <esosman@comcast-dot-net.invalid> - 2015-08-13 08:25 -0400
            Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") leif.roar@dimnakorr.com - 2015-08-13 08:43 -0500
      Re: PLEASE SOLVE THIS ERROR (case 1:from=="VIJAYAWADA") Eternal Hope <laughingspam99@gmail.com> - 2015-08-10 15:39 +0100

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