Not getting Try/Catch

[JeePee]

Hello, I have been going trough the book Beginning php5 mysql and apache from Wrox. And i have trouble figuring out the following example that should illustrate the use of try/catch

<?php
//$x = "";		//Throws null Exception
//$x = "500";		//Throws less than Exception
$x = "1000";		//Throws NO Exception

try {
  if ($x == "") {
    throw new Exception("Variable cannot be null");
  }
  if ($x < 1000) {
    throw new Exception("Variable cannot be less than 1000");
  }
  echo "Validation Accepted!";
}
catch (Exception $exception) {
  echo $exception->getMessage();
  echo " - Validation Denied!";
}
?>

The explenation that comes with it does not make me any wiser eighter.
I don't see why should i not just put an echo in the if statement..

[Houdini]

Basically if you look at the code and notice that two variables are commented out. The way the code is written right now the catch will not do anything because no exception is met by the value of $x (which is 1000).
in the try function it has set up three possiblities, one where if $x is null it will output

Variable cannot be null - Validation Denied! 

then if you were to recomment it and uncomment $x=500 then the try would output

Variable cannot be less than 1000 - Validation Denied! 

and lastly the way the code is shown in your example there would be no exception and the $x=1000 would meet the condition of and value of 1000 or more and would output

Validation Accepted! 

The $x=""; and $x=500; and $x=1000 are just so you can see what happens with different values passed to the try.

Comment out the $x=1000; and uncomment one of the other two $x assignments and see what happens when you run that code and you will start to see how the try catch is used.