Java ArrayList to single string without using loop

Question

I have an ArrayList<String> that is added to periodically. What I want to do is to cast the entire ArrayList to a String without doing a loop. Can anybody tell me is it possible without using loop?

Edited: So we found some solutions, Like

list.stream().collect(Collectors.joining());

Or

String result = String.join(",", list);

or some others as well. Now Just for getting knowledge I put a question which one is the most optimal way for compiler?

`arrayList.stream().collect(Collectors.joining(", "))` is one of the options. — MC Emperor, Jun 03 '19 at 20:38
Any option, no matter how fancy it looks, will use a loop under the hood. Use a loop and go for the most straightforward and idiomatic implementation, that will be the best to do here. — Zabuzard, Jun 03 '19 at 20:40
"Best optimal solution" - You will not find a faster solution, all solutions somehow need to iterate through all items once. You can stream it for adding multi-threading to it. But the list needs to be huge for that to pay off. — Zabuzard, Jun 03 '19 at 20:45
You could always use Apache commons library, where it’s just ‘StringUtils.join(list, ", ")’ — racraman, Jun 03 '19 at 20:46

Michał Krzywański · Accepted Answer · 2019-06-03T20:46:46.523

5

You could make a stream out of your list and collect it using joining collector :

list.stream().collect(Collectors.joining());

You can pass the separator to Collectors::joining method for example :

list.stream().collect(Collectors.joining("-"));

Or you can use String::join method :

String result = String.join(",", list);

where , is the separator.

edited Jun 03 '19 at 20:46

answered Jun 03 '19 at 20:40

Michał Krzywański

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score 2 · Answer 2 · edited Jun 03 '19 at 20:51

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Given some ArrayList<String> s, all you need to use to get a String representation is s.toString().

The format is the following

[element1, element2, element3]

edited Jun 03 '19 at 20:51

Yassin Hajaj

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answered Jun 03 '19 at 20:38

Ben I.

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To expand: what you get from ArrayList.toStirng is a comma-separated list of elements, enclosed in brackets. (Of course, there probably is a loop involved, just not one that you have to write) – Jun 03 '19 at 20:47

score 2 · Answer 3 · answered Jun 03 '19 at 20:40

2

I Believe you can do

String.join(", ", list);

Hope this helps :)

answered Jun 03 '19 at 20:40

Damian

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Java ArrayList to single string without using loop

3 Answers3