Flatten a Stream of Arrays in Java using forEach loop
Given a Stream of Arrays in Java, the task is to Flatten the Stream using forEach() method.
Examples:
Input: arr[][] = {{ 1, 2 }, { 3, 4, 5, 6 }, { 7, 8, 9 }}
Output: [1, 2, 3, 4, 5, 6, 7, 8, 9]
Input: arr[][] = {{'G', 'e', 'e', 'k', 's'}, {'F', 'o', 'r'}}
Output: [G, e, e, k, s, F, o, r]
Approach:
- Get the Arrays in the form of 2D array.
- Create an empty list to collect the flattened elements.
- With the help of forEach loop, convert each elements of the array into stream and add it to the list
- Now convert this list into stream using stream() method.
- Now flatten the stream by converting it into array using toArray() method.
Below is the implementation of the above approach:
Example 1: Using arrays of integer.
// Java program to flatten a stream of arrays// using forEach() method  import java.util.ArrayList;import java.util.Arrays;import java.util.List;import java.util.stream.Stream;  class GFG {      // Function to flatten a Stream of Arrays    public static <T> Stream<T> flattenStream(T[][] arrays)    {          // Create an empty list to collect the stream        List<T> list = new ArrayList<>();          // Using forEach loop        // convert the array into stream        // and add the stream into list        for (T[] array : arrays) {            Arrays.stream(array)                .forEach(list::add);        }          // Convert the list into Stream and return it        return list.stream();    }      public static void main(String[] args)    {          // Get the arrays to be flattened.        Integer[][] arr = {            { 1, 2 },            { 3, 4, 5, 6 },            { 7, 8, 9 }        };          // Flatten the Stream        Integer[] flatArray = flattenStream(arr)                                  .toArray(Integer[] ::new);          // Print the flattened array        System.out.println(Arrays.toString(flatArray));    }} |
Output:
[1, 2, 3, 4, 5, 6, 7, 8, 9]
Example 2: Using arrays of Characters.
// Java program to flatten a stream of arrays// using forEach() method  import java.util.ArrayList;import java.util.Arrays;import java.util.List;import java.util.stream.Stream;  class GFG {      // Function to flatten a Stream of Arrays    public static <T> Stream<T> flattenStream(T[][] arrays)    {          // Create an empty list to collect the stream        List<T> list = new ArrayList<>();          // Using forEach loop        // convert the array into stream        // and add the stream into list        for (T[] array : arrays) {            Arrays.stream(array)                .forEach(list::add);        }          // Convert the list into Stream and return it        return list.stream();    }      public static void main(String[] args)    {          // Get the arrays to be flattened.        Character[][] arr = {            { 'G', 'e', 'e', 'k', 's' },            { 'F', 'o', 'r' },            { 'G', 'e', 'e', 'k', 's' }        };          // Flatten the Stream        Character[] flatArray = flattenStream(arr)                                    .toArray(Character[] ::new);          // Print the flattened array        System.out.println(Arrays.toString(flatArray));    }} |
Output:
[G, e, e, k, s, F, o, r, G, e, e, k, s]
