Flatten a Stream of Arrays in Java using forEach loop
Last Updated : 11 Dec, 2018
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 // 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 // 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]
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