java - Convert String ArrayList to String Array with bigger size

Question

I am trying to convert Array list to String array but getting an exception. Can somebody please help me.

Size of ArrayList: 1
Size of String Array: 2

I am using the following code:

String[] StringArray ={};
StringArray = ArrayList.toArray(new String[ArrayList.size()]);

So, the length of StringArray now is 1. But it should be 2. My problem is how can i convert arraylist to StringArray if String Array size is more than the ArrayList.

How can i do that? Please guys help me.

That would not compile: `toArray` is not a static method of the `ArrayList` class. Is that your real code? — assylias, May 22 '13 at 12:00
possible duplicate of [convert String arraylist to string array in java?](http://stackoverflow.com/questions/4042434/convert-string-arraylist-to-string-array-in-java) — Alexis C., May 22 '13 at 12:01
I think, that there is no statis call... he just named variables ArrayList and StringArray — Martin Perry, May 22 '13 at 12:02
no, its not a duplicate of the question linked. My problem is how can i convert arraylist to StringArray if String Array size is more than the ArrayList. Guys please help me. — Avadhani Y, May 22 '13 at 12:04
@Aʌɐpɥɐuı Show all the relevant code (how you create the list, how you determine the sizes etc.). — assylias, May 22 '13 at 12:05
Old StringArray size is ommited in moment, you make "=" from toArray — Martin Perry, May 22 '13 at 12:05
@Aʌɐpɥɐuı With the code you show, StringArray should be the same size as `nameValuesTestImage` at the end. — assylias, May 22 '13 at 12:10
bad naming conventions. Variable names should not start with capitals unless your looking to confuse reviewers and helpers! — tgkprog, May 22 '13 at 12:33

BobTheBuilder · Accepted Answer · 2013-05-22T12:35:43.733

If you want to convert ArrayList to a bigger String array, use toArray() and pass the array you want to fill as parameter. If the array size is more than needed, the rest of the elements will be null. If the array is smaller - a new array will be returned with size as list.size.

All taken from javadoc

ArrayList<String> list  = new ArrayList<>();
list.add("abc");

String[] StringArray = new String[2];
StringArray = list.toArray(StringArray);

In that case, even though the list size is 1, StringArray is of size 2, adding null values at the end of the array.

score 0 · Answer 2 · answered May 22 '13 at 12:05

0

 String[] arr = new String[list.size()];
 arr = list.toArray(arr);

answered May 22 '13 at 12:05

Juned Ahsan

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score 0 · Answer 3 · answered May 22 '13 at 12:06

0

Try to do it like in this tutorial: http://viralpatel.net/blogs/convert-arraylist-to-arrays-in-java/

The size of array defined before .toArray method has no effect on result. After calling .toArray, old array is destroyed by JVM.

answered May 22 '13 at 12:06

Martin Perry

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score 0 · Answer 4 · answered Jun 23 '15 at 11:35

If we pass an array as argument to method toArray then it populates that with the items of list else it returns an array of Object. We can pass an array of size larger than the list as argument to get an array of greater size. The following example explains it:

     public static void main(String[] args) throws FileNotFoundException {
        List<String> list  = new ArrayList<>();
        list.add("One");
        System.out.println("list Size: " + list.size());

        //If we pass an array as argument it will be filled with items from list and then returned. Here array size is (list.size +2 )
        String[] stringArray = list.toArray(new String[2]);
        System.out.println("stringArray Size: " + stringArray.length);

        //If we do not pass an array as argument we get Object[] of same size
        Object[] objects = list.toArray();
        System.out.println("objects Size: " + objects.length);

        // Java 8 has option of streams to get same size array
        String[] stringArrayUsingStream = list.stream().toArray(String[]::new);
        System.out.println("stringArrayUsingStream Size: " + stringArrayUsingStream.length);
    }

As shown above we have an option of using streams also in Java 8. The output is:

list Size: 1 stringArray Size: 2 objects Size: 1 stringArrayUsingStream Size: 1

java - Convert String ArrayList to String Array with bigger size

4 Answers4