Adding effects when full armor is on!?

Hey i have this code, yes I know how to add effects when armor is on but how can I make it so that it only adds effect when a full iron armor set is put on. Heres the function

PHP:

 public function onArmor(EntityChangeArmorEvent $e){

$entity = $e->getEntity();
//We now use if statements and check if $entity is an instanceof Player.

if($entity instanceof Player){
if(//Code to check helmet, chestplate and leggings goes here){


 

I dont know how to check the whole armor suit please help

 

check if helmet, chestplate, leggings, boots is not equal to null

 

I get that, but how can I make it so that it only gives effects when it has CHESTPLATE HELMET LEGGINGS AND BOOTS. Like provide a function I tried using

GOLD_HELMET && GOLD_CHESTPLATE but it didnt work please help

 

Check if the ID is equal to that

 

Can you please just give me simple example code? I cant really understand what you mean. I get it but I dont know what you mean like clearly please help.

 

Why are you being like this? Isnt this the point? I simply dont know how to check for null and atuff im new. I can make other functions and stuff. If you would have taught me I could have used for some othernstuff like I do with all the other stuff other people help me with. Seriously dude thats messed up