<?php

class SomeException extends Exception {}
class SomeClass{
  function validate($data){
    throw new SomeException("Invalid data");
  }
}

$o = new SomeClass();
$someData = 123;

try{
  $o->validate($someData);
  echo "do somthing";
} catch (SomeException $e) {
  echo $e->getMessage();
}

Invalid data