Java - Filter prime number from an infinite stream of natural numbers

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Introduction

To get the first five prime numbers.

You can generate an infinite stream of natural numbers, apply a filter operation to pick only the prime numbers, and limit the filtered stream to five.

The following code shows this logic using the isPrime() method of the PrimeUtil class:

Demo

import java.util.stream.Stream;

public class Main {
  public static void main(String[] args) {
    // Print the first 5 prime numbers
    Stream.iterate(2L, n -> n + 1)
          .filter(PrimeUtil::isPrime)/*from   w w w  .j a  va  2  s. c o m*/
          .limit(5)
          .forEach(System.out::println);
  }
}

class PrimeUtil {
  private long lastPrime = 0L;

  // Computes the prime number after the last generated prime
  public long next() {
    lastPrime = next(lastPrime);
    return lastPrime;
  }

  // Computes the prime number after the specified number
  public static long next(long after) {
    long counter = after;

    // Keep looping until you find the next prime number
    while (!isPrime(++counter))
      ;

    return counter;
  }
  // Checks if the specified number is a prime number
  public static boolean isPrime(long number) {
    // <= 1 is not a prime number
    if (number <= 1) {
      return false;
    }

    // 2 is a prime number
    if (number == 2) {
      return true;
    }

    // Even numbers > 2 are not prime numbers
    if (number % 2 == 0) {
      return false;
    }

    long maxDivisor = (long) Math.sqrt(number);
    for (int counter = 3; counter <= maxDivisor; counter += 2) {
      if (number % counter == 0) {
        return false;
      }
    }

    return true;
  }
}

Result

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