Question

Let’s say I have a Node class. It has a single field, Node parentNode. It’s got setters and getters too.

I have 2 nodes: Node nodeA and Node nodeB.

Here’s what I want to do: set nodeB‘s parent to nodeA‘s parent, and then set nodeA‘s parent to null.

1. nodeB.setParent(nodeA.getParent());
2. nodeA.setParent(null); // bad since nodeB.getParent() will = null

To achieve the above, must I clone nodeA, and then do nodeB.setParent(nodeAClone.getParent())?

Answer 1

nodeA.setParent(null); // bad since nodeB.getParent() will = null

No, nodeB.parent will not be set to null. Java always uses Pass by Value and not pass by reference. Repeat it 10 times.

And in case you pass references, you pass them by value of references.

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Let’s understand in more detail.

When you do: –

nodeB.setParent(nodeA.getParent());

you simply create a copy of reference to nodeA parent, and store it in nodeB parent. So, you have now two references referring to nodeA parent object.Now, when you set nodeA parent to null, it is detached from that parent, but nodeB parent reference is still there.