[java] Converting 'ArrayList<String> to 'String[]' in Java

How might I convert an ArrayList<String> object to a String[] array in Java?

List <String> list = ...
String[] array = new String[list.size()];
int i=0;
for(String s: list){
  array[i++] = s;
}

In Java 8:

String[] strings = list.parallelStream().toArray(String[]::new);

We have following three ways for converting arraylist to array

1. 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);

2. 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

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)

from java.base's java.util.Collection.toArray().

    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 is converted to a String stream. Then it uses Stream.toArray to convert the elements in the stream to an Array. In the last statement above "size -> new String[size]" is actually an IntFunction function that allocates a String array with the size of the String stream. The statement is identical to

IntFunction<String []> allocateFunc = size -> { 
return new String[size];
};   
String [] strArry= list.stream().toArray(allocateFunc);

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.

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.

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]);
    }

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.

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;
}

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);

In Java 8, it can be done using

String[] arrayFromList = fromlist.stream().toArray(String[]::new);

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!

An alternative in Java 8:

String[] strings = list.stream().toArray(String[]::new);

Java 11+:

String[] strings = list.toArray(String[]::new);

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()));
  }
}

Starting from Java-11, one can alternatively 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