improving a routing class* - php

Question

I use the class below to route all requests for php on my web application. Can I improve upon this?
/*route*/
class route
{
function __construct($a)
{
if(isset($_FILES['ufile']['tmp_name'])) // handles file uploads
{
new upload();
}
elseif(isset($_POST['a'])) // handles AJAX
{
$b=$_POST['a'];
switch($b)
{
case '0':
new signin();
break;
case '1':
new signup();
break;
case '2':
session::finish();
break;
case '3':
new bookmark('insert');
break;
case '3a':
new bookmark('delete');
break;
case '4':
new tweet();
break;
default:
echo "ajax route not found";
break;
}
}
elseif($a!=0) // handles views
{
new view($a);
}
else
{
// route not found
}
}
}
Verification(passes)
/*ROUTE
// Test Code - create entry
new route(0);
new route(1);
$_FILES['ufile']['tmp_name']='test file';
new route(0);
unset($_FILES['ufile']['tmp_name']);
$_POST['a']=0;
new route(0);
// Test Cases
// Case 0: echo "not routed: <br>";
// Case 1: echo "view created: $a <br>";
// Case 2: echo "file uploaded <br>";
// Case 3: echo "ajax responded: <br>";
*/

Answer 1

public static function route($a)
{
// The first if statement is redundant this line will accomplish the
// same as the if/else because if post[a] is not set it will become null
$b=$_POST["a"];
// now that b is a, it's really one switch statement
if( $b==0 && $a==0 )
switch( $b )
{
case '0':
new signin();
break;
case '1':
new signup();
general::upload();
break;
case '2':
session::finish();
break;
case '3':
new bookmark('insert');
break;
case '3a':
new bookmark('delete');
break;
case '4':
new tweet();
break;
default:
view::posts_all();
break
}
}elseif( $a==1 )
view::bookmarks();
else
view::posts_all();
Give that a go, Good luck. (A side note: the quotation marks on the numeric cases are optional, the 3a is not. I left them in there because they were in the original. You could reduce it further by getting rid of $b entirely and running the switch on $_POST['a'] )

Answer 2

if/else statement lets you set particular condition evaluations, while switch/case only lets you set some particular values that the variable may assume (i.e. in a switch/case you cannot say something like $b > 10).
Except for that, there's no much difference between if/else or switch/case.
I suggest you to you use switch/case construct, since you are just comparing $b with a group of constants.
Besides, remember premature optimization is the root of all evil :)