Converting 'ArrayList<String> to 'String[]' in Java
JavaArraysStringArraylistCollectionsJava Problem Overview
How might I convert an ArrayList<String>
object to a String[]
array in Java?
Java Solutions
Solution 1 - Java
List<String> list = ..;
String[] array = list.toArray(new String[0]);
For example:
List<String> list = new ArrayList<String>();
//add some stuff
list.add("android");
list.add("apple");
String[] stringArray = list.toArray(new String[0]);
The toArray()
method without passing any argument returns Object[]
. So you have to pass an array as an argument, which will be filled with the data from the list, and returned. You can pass an empty array as well, but you can also pass an array with the desired size.
Important update: Originally the code above used new String[list.size()]
. However, this blogpost reveals that due to JVM optimizations, using new String[0]
is better now.
Solution 2 - Java
An alternative in Java 8:
String[] strings = list.stream().toArray(String[]::new);
Java 11+:
String[] strings = list.toArray(String[]::new);
Solution 3 - Java
You can use the toArray()
method for List
:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = list.toArray(new String[list.size()]);
Or you can manually add the elements to an array:
ArrayList<String> list = new ArrayList<String>();
list.add("apple");
list.add("banana");
String[] array = new String[list.size()];
for (int i = 0; i < list.size(); i++) {
array[i] = list.get(i);
}
Hope this helps!
Solution 4 - Java
Starting from Java-11, one can use the API Collection.toArray(IntFunction<T[]> generator)
to achieve the same as:
List<String> list = List.of("x","y","z");
String[] arrayBeforeJDK11 = list.toArray(new String[0]);
String[] arrayAfterJDK11 = list.toArray(String[]::new); // similar to Stream.toArray
Solution 5 - Java
ArrayList<String> arrayList = new ArrayList<String>();
Object[] objectList = arrayList.toArray();
String[] stringArray = Arrays.copyOf(objectList,objectList.length,String[].class);
Using copyOf, ArrayList to arrays might be done also.
Solution 6 - Java
In Java 8:
String[] strings = list.parallelStream().toArray(String[]::new);
Solution 7 - Java
In Java 8, it can be done using
String[] arrayFromList = fromlist.stream().toArray(String[]::new);
Solution 8 - Java
Generics solution to covert any List<Type>
to String []
:
public static <T> String[] listToArray(List<T> list) {
String [] array = new String[list.size()];
for (int i = 0; i < array.length; i++)
array[i] = list.get(i).toString();
return array;
}
Note You must override toString()
method.
class Car {
private String name;
public Car(String name) {
this.name = name;
}
public String toString() {
return name;
}
}
final List<Car> carList = new ArrayList<Car>();
carList.add(new Car("BMW"))
carList.add(new Car("Mercedes"))
carList.add(new Car("Skoda"))
final String[] carArray = listToArray(carList);
Solution 9 - Java
You can use Iterator<String>
to iterate the elements of the ArrayList<String>
:
ArrayList<String> list = new ArrayList<>();
String[] array = new String[list.size()];
int i = 0;
for (Iterator<String> iterator = list.iterator(); iterator.hasNext(); i++) {
array[i] = iterator.next();
}
Now you can retrive elements from String[]
using any Loop.
Solution 10 - Java
If your application is already using Apache Commons lib, you can slightly modify the accepted answer to not create a new empty array each time:
List<String> list = ..;
String[] array = list.toArray(ArrayUtils.EMPTY_STRING_ARRAY);
// or if using static import
String[] array = list.toArray(EMPTY_STRING_ARRAY);
There are a few more preallocated empty arrays of different types in ArrayUtils
.
Also we can trick JVM to create en empty array for us this way:
String[] array = list.toArray(ArrayUtils.toArray());
// or if using static import
String[] array = list.toArray(toArray());
But there's really no advantage this way, just a matter of taste, IMO.
Solution 11 - Java
List <String> list = ...
String[] array = new String[list.size()];
int i=0;
for(String s: list){
array[i++] = s;
}
Solution 12 - Java
in case some extra manipulation of the data is desired, for which the user wants a function, this approach is not perfect (as it requires passing the class of the element as second parameter), but works:
import java.util.ArrayList; import java.lang.reflect.Array;
public class Test {
public static void main(String[] args) {
ArrayList<Integer> al = new ArrayList<>();
al.add(1);
al.add(2);
Integer[] arr = convert(al, Integer.class);
for (int i=0; i<arr.length; i++)
System.out.println(arr[i]);
}
public static <T> T[] convert(ArrayList<T> al, Class clazz) {
return (T[]) al.toArray((T[])Array.newInstance(clazz, al.size()));
}
}
Solution 13 - Java
In Java 11, we can use the Collection.toArray(generator)
method. The following code will create a new array of strings:
List<String> list = List.of("one", "two", "three");
String[] array = list.toArray(String[]::new)
Solution 14 - Java
List<String> list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");
String [] strArry= list.stream().toArray(size -> new String[size]);
Per comments, I have added a paragraph to explain how the conversion works.
First, List
IntFunction<String []> allocateFunc = size -> {
return new String[size];
};
String [] strArry= list.stream().toArray(allocateFunc);
Solution 15 - Java
You can convert List to String array by using this method:
Object[] stringlist=list.toArray();
The complete example:
ArrayList<String> list=new ArrayList<>();
list.add("Abc");
list.add("xyz");
Object[] stringlist=list.toArray();
for(int i = 0; i < stringlist.length ; i++)
{
Log.wtf("list data:",(String)stringlist[i]);
}
Solution 16 - Java
private String[] prepareDeliveryArray(List<DeliveryServiceModel> deliveryServices) {
String[] delivery = new String[deliveryServices.size()];
for (int i = 0; i < deliveryServices.size(); i++) {
delivery[i] = deliveryServices.get(i).getName();
}
return delivery;
}
Solution 17 - Java
We have following three ways for converting arraylist to array
-
public
T[] toArray(T[] a) - In this way we will create a array with size of list then put in method as String[] arr = new String[list.size()]; arr = list.toArray(arr);
-
Public get() method - In this way we iterate list and put element in array one by one
Reference : How to convert ArrayList To Array In Java