How to convert a List<String> into a comma separated string without iterating List explicitly [duplicate]

Question

List<String> ids = new ArrayList<String>(); ids.add("1"); ids.add("2"); ids.add("3"); ids.add("4"); 

Now i want an output from this list as 1,2,3,4 without explicitly iterating over it.

Answer 1

On Android use:

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

Answer 2

With Java 8:

String csv = String.join(",", ids); 

With Java 7-, there is a dirty way (note: it works only if you don't insert strings which contain ", " in your list) - obviously, List#toString will perform a loop to create idList but it does not appear in your code:

List<String> ids = new ArrayList<String>(); ids.add("1"); ids.add("2"); ids.add("3"); ids.add("4"); String idList = ids.toString(); String csv = idList.substring(1, idList.length() - 1).replace(", ", ",");