🧩 The core idea:

When you call a method in Java, what gets passed is a copy of the reference to the object in memory — not the object itself, but not a deep copy either.

That means both variables (the one in your service, and the one inside your helper) point to the same exact object stored in the heap.

🧠 Step-by-step example with your code

You have this line:

offerAdminMapperHelper.setCreateRelations(offerCreateAdminRequest, offer);

Let’s look at what’s going on under the hood.

1️⃣ When you create the offer object

Offer offer = offerAdminMapper.toEntity(product);

At this moment, a new Offer object is created somewhere in the heap memory.

Imagine the JVM creates it and gives it an address — let’s say 0xABC123.

In the JVM’s memory:

Heap:
  Offer@0xABC123 {
    organization = null
    user = null
    employee = null
    accountManager = null
  }

Stack (your createOffer() method):
  offer → points to 0xABC123

So your local variable offer doesn’t contain the Offer itself —

it contains a reference (a kind of “pointer”) that says “the Offer lives at address 0xABC123”.

2️⃣ You call the helper method

offerAdminMapperHelper.setCreateRelations(offerCreateAdminRequest, offer);