Java11 - Collections to Array

Java11 enhanced toArray() method to support with Argument IntFunction.

toArray is an default method added to java.util.collection interface.

It used an easy way to convert Collections to Array with a simplified process.

Let’s see how to convert the collection to the array before java11.

We have two options as given below to convert to array.

    Object[] toArray();
    <T> T[] toArray(T[] a);

One way is using toArray(), which returns Object Array, Another way using call toArray using create an empty string with the size of a collection. Here is an example in the java10 version

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class java11toArray {
    public static void main(String[] args) {
        List<String> numbers = new ArrayList<>();
        numbers.add("one");
        numbers.add("two");
        numbers.add("three");
        // Before java 11 version
        Object[] objArray = numbers.toArray();
        System.out.println(Arrays.toString(objArray));

        String[] numbersArray = numbers.toArray(new String[numbers.size()]);
        System.out.println(numbersArray);

    }
}

Java11 simplified with toArray default method.

    default <T> T[] toArray(IntFunction<T[]> generator) {

Here is a java11 toArray example to convert the collection into Array of String

import java.util.ArrayList;
import java.util.List;

public class java11toArray {
    public static void main(String[] args) {
        List<String> numbers = new ArrayList<>();
        numbers.add("one");
        numbers.add("two");
        numbers.add("three");
        String[] numbersArray = numbers.toArray(String[]::new);
    }
}