I have an Array and an ArrayList like below
String[] stringArray = new String[] {"a","b","c","d","e"};
List<String> stringList = new ArrayList<>();
stringList.add("p");
stringList.add("q");
stringList.add("r");
I want to copy stringList to stringArray. I tried with ArrayList.toArray() method but it set null to fourth element of Array. Is there any way I can do this by without using a for loop
Expected O/P
{"p","q","r","d","e"}
If you want to just overwrite existing elements in the stringArray, without touching those at farther indexes, use System#arraycopy(Object, int, Object, int, int):
// Convert list to array
String[] stringListAsArray = stringList.toArray(new String[] {});
// Copy
System.arraycopy(stringListAsArray, 0,
stringArray, 0, stringListAsArray.length);
Also, make sure the stringList is not longer than stringArray or you'll get IndexOutOfBoundsExceptions.
Array has static memory declaration thus you cannot increase the number cells.
to do this, you can convert the stringArray to list using Arrays.asList(stringArray);
then add the two lists and finally convert it back to an array.
ArrayList.toArray behaves as you saw (setting the element following the end of the List to null) :
* <p>If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list), the element in
* the array immediately following the end of the collection is set to
* <tt>null</tt>. (This is useful in determining the length of the
* list <i>only</i> if the caller knows that the list does not contain
* any null elements.)
You could convert the List to a new array and then copy that array to the start of the original array.
String arr2 = stringList.toArray(new String[stringList.size()]);
System.arraycopy (arr2, 0, stringArray, 0, arr2.length);
If your stringList contains less or equal number of Strings like your stringArray you can do it like this:
for (int i = 0; i < stringList.size(); i++) {
stringArray[i] = stringList.get(i);
}
Update This way will either update the existing array or use the generated array from the list if it contains more values
String[] listAsArray = stringList.toArray(new String[stringList.size()]);
if (listAsArray.length <= stringArray.length) {
for (int i = 0; i < listAsArray.length; i++) {
stringArray[i] = listAsArray[i];
}
} else {
stringArray = listAsArray;
}
