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.
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1How do you convert a random Object into a String?assylias– assylias2013-02-08 13:07:30 +00:00Commented Feb 8, 2013 at 13:07
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toString is (in most classes) purely intended for diagnostic messages, not "production".Hot Licks– Hot Licks2013-02-08 13:08:57 +00:00Commented Feb 8, 2013 at 13:08
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I want convert all list in String[] without iterate over it.calbertts– calbertts2013-02-08 13:09:26 +00:00Commented Feb 8, 2013 at 13:09
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Did you look at the spec for List? (I'm guessing not, otherwise you would have noticed toArray.)Hot Licks– Hot Licks2013-02-08 13:10:17 +00:00Commented Feb 8, 2013 at 13:10
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Java 8 : stackoverflow.com/a/31002358/1216775akhil_mittal– akhil_mittal2019-09-03 04:02:57 +00:00Commented Sep 3, 2019 at 4:02
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7 Answers
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]);
1 Comment
Alexander Pogrebnyak
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.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);
4 Comments
sundar
Why additional array copy when
objectArray can still be used as String[]?
Steve Chambers
See the bottom part of the linked question - casting
objectArray to String[] causes a ClassCastException. This answer explains better: stackoverflow.com/a/1018774/1063716sundar
Yes in case of List containing objects other than string. But that happens even in your code.
sundar
List<Object> lst = new ArrayList<Object>(); lst.add(1); I m getting ArrayStoreException for this test case.Java 8
Java 8 has the option of using streams as well.
List<Object> lst = new ArrayList<>();
lst.add("Apple");
String[] strings = lst.stream().toArray(String[]::new);
System.out.println(Arrays.toString(strings)); // [Apple]
If we have a stream of Object, we would need an intermediate operation to do object-to-string conversion, and a terminal operation to collect the results. We can use Objects.toString(obj, null) or any other such implementation for string conversion.
String[] output = lst.stream()
.map((obj) -> Objects.toString(obj, null))
.toArray(String[]::new);
1 Comment
BugsOverflow
I had to do myObjects.stream().map(myObj::toString).toArray(String[]::new);
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));
Comments
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));
answered Feb 8, 2013 at 19:05
Srujan Kumar Gulla
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Comments
There is a simple way available in Kotlin
var lst: List<Object> = ...
listOFStrings: ArrayList<String> = (lst!!.map { it.name })
