Convert List

Question

I need to convert from List<Object> to String[].

I made:

List<Object> lst ...
String arr = lst.toString();

But I got this string:

["...", "...", "..."]

is just one string, but I need String[]

Thanks a lot.

toString is (in most classes) purely intended for diagnostic messages, not "production". — Hot Licks, Feb 08 '13 at 13:08
I want convert all list in String[] without iterate over it. — calbertts, Feb 08 '13 at 13:09
Did you look at the spec for List? (I'm guessing not, otherwise you would have noticed toArray.) — Hot Licks, Feb 08 '13 at 13:10

score 27 · Accepted Answer · answered Feb 08 '13 at 13:08

27

You have to loop through the list and fill your String[].

String[] array = new String[lst.size()];
int index = 0;
for (Object value : lst) {
  array[index] = (String) value;
  index++;
}

If the list would be of String values, List then this would be as simple as calling lst.toArray(new String[0]);

answered Feb 08 '13 at 13:08

Dan D.

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Change `array[index] = (String) value`, to `array[index] = String.valueOf( value )`. The answer as it is will crash if the list contains anything, but Strings. Maybe this is what OP wants. – Alexander Pogrebnyak Feb 08 '13 at 13:13

score 14 · Answer 2 · edited May 23 '17 at 11:53

14

You could use toArray() to convert into an array of Objects followed by this method to convert the array of Objects into an array of Strings:

Object[] objectArray = lst.toArray();
String[] stringArray = Arrays.copyOf(objectArray, objectArray.length, String[].class);

edited May 23 '17 at 11:53

Community

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answered Feb 08 '13 at 13:12

Steve Chambers

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Why additional array copy when `objectArray` can still be used as String[]? – sundar Feb 08 '13 at 13:26
See the bottom part of the linked question - casting `objectArray` to `String[]` causes a `ClassCastException`. This answer explains better: http://stackoverflow.com/a/1018774/1063716 – Steve Chambers Feb 08 '13 at 13:33
Yes in case of List containing objects other than string. But that happens even in your code. – sundar Feb 08 '13 at 13:35
3

`List – sundar Feb 08 '13 at 13:38

score 10 · Answer 3 · answered Jun 23 '15 at 12:06

10

Java 8 has the option of using streams like:

List<Object> lst = new ArrayList<>();
String[] strings = lst.stream().toArray(String[]::new);

answered Jun 23 '15 at 12:06

akhil_mittal

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score 5 · Answer 4 · answered Feb 08 '13 at 13:22

If we are very sure that List<Object> will contain collection of String, then probably try this.

List<Object> lst = new ArrayList<Object>();
lst.add("sample");
lst.add("simple");
String[] arr = lst.toArray(new String[] {});
System.out.println(Arrays.deepToString(arr));

score 2 · Answer 5 · answered Feb 08 '13 at 19:05

Lot of concepts here which will be useful:

List<Object> list = new ArrayList<Object>(Arrays.asList(new String[]{"Java","is","cool"}));
String[] a = new String[list.size()];
list.toArray(a);

Tip to print array of Strings:

System.out.println(Arrays.toString(a));

score 2 · Answer 6 · answered Jul 17 '13 at 13:13

2

Using Guava

List<Object> lst ...    
List<String> ls = Lists.transform(lst, Functions.toStringFunction());

answered Jul 17 '13 at 13:13

husayt

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score 0 · Answer 7 · edited Feb 11 '21 at 22:41

0

There is a simple way available in Kotlin

var lst: List<Object> = ...
    
listOFStrings: ArrayList<String> = (lst!!.map { it.name })

edited Feb 11 '21 at 22:41

flaxel

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answered Feb 11 '21 at 13:05

Umasankar

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Convert List

7 Answers7

Linked