The problem
In this exercise display all the prime numbers between 2 and 1,000, inclusive. Display eight prime numbers per line. Numbers are separated by exactly one space.
Breaking it down
Creating a range of numbers using java 8 IntStream and filtering numbers in stream calling a method that will check if the number is prime will leave us with a list of numbers. Next since the requirements of the exercise stated to show eight per line, we can split the list which will leave a List of List of a size of eight.
final static int PRIMES_PER_LINE = 10;
public static void main(String[] args) {
List<Integer> primeNumbers = IntStream.rangeClosed(0, 1000)
.filter(i -> isPrime(i)).boxed().collect(Collectors.toList());
List<List<Integer>> primesBy10 = Lists.partition(primeNumbers,
PRIMES_PER_LINE);
Stream.of(primesBy10).flatMap(l -> l.stream())
.forEach(System.out::println);
static boolean isPrime(int n) {
for (int i = 2; 2 * i < n; i++) {
if (n % i == 0)
return false;
}
return true;
}
}Output
[0, 1, 2, 3, 4, 5, 7, 11, 13, 17]
[19, 23, 29, 31, 37, 41, 43, 47, 53, 59]
[61, 67, 71, 73, 79, 83, 89, 97, 101, 103]
[107, 109, 113, 127, 131, 137, 139, 149, 151, 157]
[163, 167, 173, 179, 181, 191, 193, 197, 199, 211]
[223, 227, 229, 233, 239, 241, 251, 257, 263, 269]
[271, 277, 281, 283, 293, 307, 311, 313, 317, 331]
[337, 347, 349, 353, 359, 367, 373, 379, 383, 389]
[397, 401, 409, 419, 421, 431, 433, 439, 443, 449]
[457, 461, 463, 467, 479, 487, 491, 499, 503, 509]
[521, 523, 541, 547, 557, 563, 569, 571, 577, 587]
[593, 599, 601, 607, 613, 617, 619, 631, 641, 643]
[647, 653, 659, 661, 673, 677, 683, 691, 701, 709]
[719, 727, 733, 739, 743, 751, 757, 761, 769, 773]
[787, 797, 809, 811, 821, 823, 827, 829, 839, 853]
[857, 859, 863, 877, 881, 883, 887, 907, 911, 919]
[929, 937, 941, 947, 953, 967, 971, 977, 983, 991]
[997]