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javalistdata-structuresreferencestorage
Shailesh Tainwala
Shailesh Tainwala

Reputation: 6507

Storing an object in a list, then making changes to the object

I have an object which I add to a List using the method theList.add(theObj).

If I now make changes to this object theObj, will these changes always be reflected in the object stored in the list?

If yes, does this mean that List in java stores only references and not unique copies of the objects it is passed?

Upvotes: 1

Views: 429

Answers (2)

Brian
Brian

Reputation: 25834

If yes, does this mean that List in java stores only references and not unique copies of the objects it is passed?

Well, it will make a copy if you're using primitives. And possibly strings.

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1500495

You don't store an object in the list. You store a reference in the list.

And yes, if you make a change to the object via any reference, that change will be visible however else you get to the same object.

The same is true for assignment, argument passing etc:

StringBuilder builder = new StringBuilder();
StringBuilder builder2 = builder;

builder.append("foo");
System.out.println(builder2); // Prints foo

Here the values of builder and builder2 are references to the same StringBuilder object - so having appended a string to the data in the object via builder, you can reach the same information via builder2.

Upvotes: 11

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