How to convert List of arrays into a single array in Java. Is there any predefined function to use?
Below is the list of arrays, I want to iterate and keep all values in a single array.
List<Integer[]> integerArrayList = new ArrayList<Integer[]>();
Integer[] resultArray = {};
Is there efficient way to implement?
Java 8's stream make this pretty easy:
Integer[] resultArray =
integerArrayList.stream().flatMap(Arrays::stream).toArray(Integer[]::new);
With Streams:
Integer[] resultArray = integerArrayList.stream () // create a Stream<Integer[]>
.flatMap (Stream::of) // flatten to a Stream<Integer>
.toArray (Integer[]::new); // generate Integer[]
Similarly, you can produce an int[]:
int[] resultArray2 = integerArrayList.stream () // create a Stream<Integer[]>
.flatMap (Stream::of) // flatten to a Stream<Integer>
.mapToInt(Integer::intValue) // convert to IntStream
.toArray (); // generate int[]
