Does the iterator give me a deep copy?

Question

I hope I am just confused now because my Java program behaves strange.

I have the following code:

Iterator<Entry<DateTime, Double>> itCur = this.curIntervalValues.entrySet().iterator();

Entry<DateTime, Double> last = null;
while (itCur.hasNext()){
  Entry<DateTime, Double> curr =  itCur.next();
  //more code between
  last = curr;
}

My question is quite simple: does last = curr; makes a deep copy of curr? Or does last now every time changes if curr changes?

You haven't said how your Java program behaves, or what `curIntervalValues` is, or in what way you expect `curr` to change. It would help if you could post a short but complete program demonstrating the problem. — Jon Skeet, Jul 09 '13 at 15:30
Exactly it is regular behavior - you're working not with objects, but with reference objects. — bsiamionau, Jul 09 '13 at 15:33
@zvzdhk you mean that the regular behavior is the statement in second question at bottom. — Luiggi Mendoza, Jul 09 '13 at 15:34
@LuiggiMendoza I mean that her Java program does not behave strange. — bsiamionau, Jul 09 '13 at 15:55

score 4 · Accepted Answer · edited May 23 '17 at 12:31

4

When executing last = curr, last won't be a copy of the current item, it will be the current item reference. So if you edit its fields, you will edit the fields of the curr object reference as well. For example, if you execute

System.out.println(last.getSomeProperty());
last.setSomeProperty(newValue);
System.out.println(last.getSomeProperty());

It will print

oldValue
newValue

And your reference will be modified in your collection as well.

does last now every time changes if curr changes?

Short answer: yes.

By your comment, looks like you want a clone of the data handled by curr. If so, I would recommend following one of the approaches stated here: Java: recommended solution for deep cloning/copying an instance

edited May 23 '17 at 12:31

Community

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answered Jul 09 '13 at 15:31

Luiggi Mendoza

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Thanks for your answer! Is there an easy way to make a deep copy of curr? – cruxi Jul 09 '13 at 15:38
@cruxi answer updated. Please refer to the link I've provided. – Luiggi Mendoza Jul 09 '13 at 15:40

score 1 · Answer 2 · answered Jul 09 '13 at 15:30

1

Entry<DateTime, Double> is an object, therefore it is stored by reference, meaning that only the object's location in memory is stored in the variable. So yes, if you do last = curr, last will change if you alter curr.

answered Jul 09 '13 at 15:30

xlecoustillier

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Does the iterator give me a deep copy?

2 Answers2