Streams on Arrays in Java 8

import java.util.Arrays;
class GFG_Demo_1 {
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
            11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };

        // Let's try the imperative style first(which we
        // are familiar with)
        int sum = 0;
        for (int i = 0; i < arr.length; i++)
            sum += arr[i];
        System.out.println("Average using iteration :" +
                                    (sum / arr.length));

        // Let's try the declarative style now
        sum = Arrays.stream(arr) // Step 1
                  .sum(); // Step 2
        System.out.println("Average using streams : " +
                                   (sum / arr.length));

        // forEach()
        // It iterates through the entire streams
        System.out.println("Printing array elements : ");
        Arrays.stream(arr)
            .forEach(e->System.out.print(e + " "));
    }
}

import java.util.Arrays;
import java.util.function.IntPredicate;
class GFG_Demo_2 {
  public static void main(String[] args)
  {
        int arr_sample1[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
                 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 };

        // asDoubleStream()
        // It converts the original array to double
        System.out.println("Example of asDoubleStream(): ");
        Arrays.stream(arr_sample1)
            .asDoubleStream()
            .forEach(e->System.out.print(e + " "));

        // asLongStream()
        // It converts the original array to Long
        System.out.println("\nExample of asLongStream");
        Arrays.stream(arr_sample1)
            .asLongStream()
            .forEach(e->System.out.print(e + " "));

        int arr_sample2[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9,
            10, 23, 12, 13, 14, 15, 16, 17, 18, 19, 20 };

        // anyMatch()
        // This method find whether the given predicate 
        // is in the array or not
        System.out.println("\nExample of anyMatch");

        // Test whether any of the element in array is 
        // divisible by 11 or not
        IntPredicate predicate = e->e % 11 == 0;
        System.out.println(Arrays.stream(arr_sample2)
                               .anyMatch(predicate));

        // You can directly write the lambda expression
        // which computes to IntPredicate
        // Uncomment to test
        // System.out.println(Arrays.stream(arr)
        // .anyMatch(e -> e % 11 == 0));

        int arr_sample3[] = { 2, 4, 6, 8, 10 };
        int arr_sample4[] = { 1, 3, 5, 7, 11 };

        // allMatch()
        // This method finds whether the given predicate 
        // matches the entire array or not
        System.out.println("Example of allMatch :");

        // Returns true as all the elements of arr_sample3
        // is even
        System.out.println(Arrays.stream(arr_sample3)
                               .allMatch(e->e % 2 == 0));

        // Returns false as all the elements of arr_sammple4
        // is odd
        System.out.println(Arrays.stream(arr_sample4)
                               .allMatch(e->e % 2 == 0));

        // noneMatch()
        System.out.println("Example of noneMatch");
        System.out.println(Arrays.stream(arr_sample4)
                               .noneMatch(e->e % 2 == 0));
    }
}

import java.util.Arrays;
class GFG_Demo_3 {
    public static void main(String[] args)
    {
        int arr_sample1[] = { 11, 2, 3, 42, 5, 6, 17, 8, 9, 
               10, 11, 12, 13, 24, 55, 16, 47, 18, 19, 20 };
        System.out.println("These method returns Optional");

        // average()
        // This method returns a average of an array
        System.out.println("Example of average() : ");
        System.out.println((Arrays.stream(arr_sample1)
                                .average()));

        // findAny()
        // It can return any value from the stream
        // Most of the time it returns the first value 
        // but it is not assured it can return any value
        System.out.println("Example of findAny() : ");
        System.out.println(Arrays.stream(arr_sample1)
                               .findAny());

        // findFirst()
        // It returns the first element of the stream
        System.out.println("Example of findFirst() :");
        System.out.println(Arrays.stream(arr_sample1)
                               .findFirst());

        // max()
        // It returns the max element in an array
        System.out.println("Example of max() :");
        System.out.println(Arrays.stream(arr_sample1)
                               .max());

        // min()
        // It returns the min element in an array
        System.out.println("Example of min() :");
        System.out.println(Arrays.stream(arr_sample1)
                               .min());

        // reduce()
        // It reduces the array by certain operation
        // Here it performs addition of array elements
        System.out.println("Example of reduce() :");
        System.out.println(Arrays.stream(arr_sample1)
                               .reduce((x, y)->x + y));

        // reduce() have another variation which we will
        // see in different example
    }
}

import java.util.Arrays;
class GFG_Demo_4 {
public static void main(String[] args)
    {
        int arr_sample1[] = { 11, 2, 3, 42, 5, 6, 17, 8, 9,
                10, 11, 12, 13, 24, 55, 16, 47, 18, 19, 20 };
        System.out.println("These method convert Optional to primitive");

        // OptionalDouble can be converted to double by using getAsDouble()
        // if average doesn't contains any value it throws NoSuchElementException
        System.out.println("Example of average() : ");
        System.out.println((Arrays.stream(arr_sample1)
                                .average()
                                .getAsDouble()));

        // OptionalInt can be converted to int by using getAsInt()
        System.out.println("Example of findAny() : ");
        System.out.println(Arrays.stream(arr_sample1)
                               .findAny()
                               .getAsInt());
    }
}