<?php
interface A {}
class B implements A {}
class C extends B {}
class D extends B implements A {}
$bRef = new ReflectionClass('B');
$cRef = new ReflectionClass('C');
$dRef = new ReflectionClass('D');
echo 'B implements A: '.($bRef->implementsInterface('A') ? 'yes' : 'no');
echo 'C implements A: '.$cRef->implementsInterface('A') ? 'yes' : 'no';
echo 'D implements A: '.$dRef->implementsInterface('A') ? 'yes' : 'no';
echo 'B subclass of A: '.$bRef->isSubclassOf('A') ? 'yes' : 'no';
echo 'C subclass of A: '.$cRef->isSubclassOf('A') ? 'yes' : 'no';
echo 'D subclass of A: '.$dRef->isSubclassOf('A') ? 'yes' : 'no';