Stream ToArray

The toArray method defined in the Stream class returns an array of the elements of the stream. The toArray is a terminal operation.

package org.wesome.java8;

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

class Apple {
    public static void main(String args[]) {
        List<String> fruits = new ArrayList<>();
        fruits.add("Macintosh");
        fruits.add("Fuji");
        fruits.add("Gala");
        fruits.add("Jonagold");

        System.out.println("*---------------------------to Array on list of Strings---------------------------*");

        /*  paas Array into a generator function    */
        String[] apples = fruits.stream().toArray(String[]::new);
        System.out.println("apples = " + Arrays.toString(apples));

        /*  paas size of the Array    */
        apples = fruits.stream().toArray(size -> new String[size]);
        System.out.println("apples = " + Arrays.toString(apples));

        System.out.println("*---------------------------String split into array---------------------------*");

        String appleName = "Macintosh, Fuji, Gala, Jonagold";
        String[] appleArray = Arrays.stream(appleName.split(",")).map(String::trim).toArray(String[]::new);
        System.out.println("appleArray = " + Arrays.toString(appleArray));

        System.out.println("*---------------------------to Array on primitive ints---------------------------*");
        int[] intStream = IntStream.rangeClosed(1, 5).toArray();
        System.out.println("intStream = " + Arrays.toString(intStream));

        System.out.println("*---------------------------convert Array back to Stream---------------------------*");
        int[] arr = new int[]{1, 2, 3, 4, 5};

        /*  Stream.of() also calls Arrays.stream() internally  */
        IntStream stream = Arrays.stream(arr);
        stream.forEach(System.out::println);

        System.out.println("*---------------------------to Array on Wrapper Integers---------------------------*");
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5);
        Integer[] integers = list.stream().toArray(Integer[]::new);
        System.out.println("integers = " + Arrays.toString(integers));

        System.out.println("*---------------------------Integers List to int array---------------------------*");
        int[] ints = list.stream().mapToInt(Integer::intValue).toArray();
        System.out.println("ints = " + Arrays.toString(ints));

        System.out.println("*---------------------------List of String Integers to int array---------------------------*");
        List<String> stringList = Arrays.asList("10", "20", "30", "40", "50");
        ints = stringList.stream().mapToInt(Integer::parseInt).toArray();
        System.out.println("ints = " + Arrays.toString(ints));

        System.out.println("*---------------------------List of Integers to String array---------------------------*");
        String[] stringInt = IntStream.rangeClosed(0, 10).mapToObj(Integer::toString).toArray(String[]::new);
        System.out.println("stringInt = " + Arrays.toString(stringInt));
    }
}

toArray function on User-defined object

package org.wesome.java8;

import lombok.AllArgsConstructor;
import lombok.Data;

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

@Data
@AllArgsConstructor
class Fruit {
    int fruitId;
    String fruitName;
    String taste;
    double price;
}

class Apple {
    public static void main(String args[]) {
        List<Fruit> fruits = Arrays.asList(new Fruit(1, "Macintosh", "sweet", 1.1), new Fruit(2, "Fuji", "sweet", 2.2), new Fruit(3, "Gala", "sour", 1.1), new Fruit(4, "Jonagold", "sour", 2.2));
        Fruit[] apples = fruits.stream().toArray(Fruit[]::new);
        System.out.println("apples = " + Arrays.toString(apples));

        System.out.println("*---------------------------convert Array back to List---------------------------*");
        List<Fruit> fruitList = Arrays.stream(apples).collect(Collectors.toList());
        System.out.println("fruitList = " + fruitList);
    }
}

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