what's a simple and elegant way to print arraylist elements separated by comma?

Question

Hi I'm writing code to print all elements from an ArrayList separated by comma, the folllowing is the method I wrote. It works. But i'm wondering if it can be simplified? And is there a more elegant way to print all elements from an ArrayList separated by some delimiter? (e.g. a method that prints an ArrayList of Strings get "Tom, Sherlock, Jack")

Thanks everyone!

public String printMyArrayList() {
    if(mylist.size() == 0)return "";
    else if(mylist.size() == 1)return mylist.get(0).toString();
    else {
        String returnStr = "";
        for (int i = 0; i < mylist.size() ; i++) {
            if(i == 0)returnStr = mylist.get(i).toString();
            else {
                returnStr = returnStr + ", " + mylist.get(i).toString();
            }
        }
        return returnStr;
    }
}

possible duplicate of [A quick and easy way to join array elements with a separator (the opposite of split) in Java](http://stackoverflow.com/questions/1978933/a-quick-and-easy-way-to-join-array-elements-with-a-separator-the-opposite-of-sp), and [What's the best way to build a string of delimited items in Java?](http://stackoverflow.com/questions/63150/whats-the-best-way-to-build-a-string-of-delimited-items-in-java) — Jongware, Apr 29 '15 at 10:07
Remember to check if `mylist` is `null` before checking the size, it may produce a `NullPointerException` otherwise — Ian2thedv, Apr 29 '15 at 10:19
@Ian2thedv and that is probably a good thing, because a list should never be null in the first place. Checking for null would hide a bug. — JB Nizet, Apr 29 '15 at 10:20
@KarolKrol: OP himself alternates between calling it *printing* and *joining*. The suggested (already working!) code is *called* `print..` but it doesn't really do that. Also: printing *could* be programmed in a different way than first joining and then printing, but there is no reason to. — Jongware, Apr 29 '15 at 12:48

score 9 · Answer 1 · edited Apr 29 '15 at 10:15

9

Using Collectors.joining from Java 8:

return list.stream()
           .map(Object::toString)
           .collect(Collectors.joining(", "));

edited Apr 29 '15 at 10:15

answered Apr 29 '15 at 10:08

JB Nizet

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score 4 · Answer 2 · answered Apr 29 '15 at 10:09

4

Another Java 8 solution using String.join:

List<String> l = Arrays.asList(new String[] {"foo", "bar", "baz"});

String joined = String.join(", ", l);

System.out.println(joined);

Output:

foo, bar, baz

answered Apr 29 '15 at 10:09

OP is using `item.toString()` which suggest that this is not List of Strings or other CharSequence so `String.join` can't be used here. – Pshemo Apr 29 '15 at 10:14
@Pshemo Sure, but that is not the point of the question. The joining is the intersting part, not converting objects to Strings. – Apr 29 '15 at 10:17
I am not saying that tit is bad solution, but since OP seems to ask how to elegantly print list of *any elements* (not only `CharSequence`) I would say that mentioning that this solution will work only for types which can be used as `List` `CharSequence[]` is quite important. – Pshemo Apr 29 '15 at 10:24

score 1 · Answer 3 · answered Apr 29 '15 at 10:07

1

A one-liner.

System.out.println(myArrayList.toString().replaceAll("\\[\\]", ""));

I.e. get the default String representation (which is [1, 2, 3]) and remove the braces.

answered Apr 29 '15 at 10:07

Kayaman

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Rahul Tripathi · Answer 4 · 2015-04-29T10:14:22.213

1

Try this:

String delimiter = "";
StringBuilder sb = new StringBuilder();
for (Item x : list) {
    sb.append(delimiter).append(x);
    delimiter = ",";
}

You can also use the Joiner class

Joiner.on(",").join(lst)

edited Apr 29 '15 at 10:14

answered Apr 29 '15 at 10:11

Rahul Tripathi

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malmling · Answer 5 · 2015-04-29T10:17:06.517

1

If you're working with android try this:

android.text.TextUtils.join(", ", listOfObjects);

else there's a util in spring framework.

org.springframework.util.StringUtils.arrayToCommaDelimitedString(listOfObjects);

edited Apr 29 '15 at 10:17

answered Apr 29 '15 at 10:12

malmling

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1

Where is `TextUtils` from? – Apr 29 '15 at 10:15
2

Which begs the question: how to elegantly implement TextUtils.join(), since it's not a standard class. – JB Nizet Apr 29 '15 at 10:16

LuigiPower · Answer 6 · 2015-04-29T10:12:04.680

-1

I don't know what you mean by "simple and elegant", but I'll go with it.

EDIT: String.join is probably the best way

DOUBLE EDIT: Don't use this, as pointed out in the comments below.

public String printMyArrayList(ArrayList<String> list)
{
   String result = "";
   for(String s : list)
   {
      result += s + ", ";
   }
   return result.substring(0, result.length()-2);
}

edited Apr 29 '15 at 10:12

answered Apr 29 '15 at 10:09

LuigiPower

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1

That is quite inefficient: it produces a lot of temporary String instances. – JB Nizet Apr 29 '15 at 10:11
1

I'll admit I should have put more thought on this one. I append the delimiter on each loop so I had to remove that last part. I'll leave this answer here as a "How not to do this" kind of thing. – LuigiPower Apr 29 '15 at 10:15

score -1 · Answer 7 · answered Apr 29 '15 at 10:10

-1

Use List#toString method. It will enclose with []. If you don't want to include [] than you can substring it.

   String listStr= list.toString();
   String withoutSym= listStr.substring(1, listStr.length()-1);

answered Apr 29 '15 at 10:10

Masudul

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what's a simple and elegant way to print arraylist elements separated by comma?

7 Answers7