Question

Let’s say I have a list of objects called “Node” inside of this -> Iterable allNodes.

Let’s say I iterated through all the nodes in allNodes and added them to its own list like so:

Iterable<Node> allNodes = dataManager.getAllNodes();
List<Node> copyOfAllNodes;
for(Node node : allNodes) {
    copyOfAllNodes.add(node);
}

Does the copy become a reference or is it a copy that doesn’t affect the original list?

Answer 1

It will become just a reference. When you perform:

copyAllNodes.add(node)

You are inserint node that is an object into copyAllNodes.

If you want a copy of the object you have other approaches. One of the approaches could be close, that is basically implement the Cloneable interface and expose clone method in order to copy the object, so you could do something like:

copyAllNodes.add(node.clone)

And this would be a copy that you could modify without any reflection on the copied object. Is good to remember that the default clone method does just a shallow copy of the object.

From documentation:

The method clone for class Object performs a specific cloning
operation. First, if the class of this object does not implement the
interface Cloneable, then a CloneNotSupportedException is thrown. Note
that all arrays are considered to implement the interface Cloneable.
Otherwise, this method creates a new instance of the class of this
object and initializes all its fields with exactly the contents of the
corresponding fields of this object, as if by assignment; the contents
of the fields are not themselves cloned. Thus, this method performs a
“shallow copy” of this object, not a “deep copy” operation.