java prime

PrimeChecker.java

  package org.example;

  import com.google.common.base.Stopwatch;

  import java.math.BigInteger;

  public class PrimeChecker {


    public static boolean checkPrime(final BigInteger given) {
      if (
        given.equals(BigInteger.ONE)
          || given.compareTo(BigInteger.valueOf(4)) < 0
          || given.mod(BigInteger.TWO).equals(BigInteger.ZERO)
      ) {
        return false;
      }

      final var max = given.sqrt().longValue();
      for (long i = 2; i < max; i += 2) {
          if (given.mod(BigInteger.valueOf(i + 1)).equals(BigInteger.ZERO)) {
            return false;
          }
      }
      return true;
    }


    public static void main(String[] args) {
      final var stopwatchTTotal = Stopwatch.createStarted();
      BigInteger[] primesBeforeList = {
        BigInteger.valueOf(60),
        BigInteger.valueOf(6000000000L),
        BigInteger.valueOf(60000000000L),
        BigInteger.TWO.pow(32),
        BigInteger.TWO.pow(40),
        BigInteger.TWO.pow(44),
        BigInteger.TWO.pow(48),
        BigInteger.TWO.pow(56),
        BigInteger.TWO.pow(64)
      };

      for (var primeBefore : primesBeforeList) {
        final var checkingFor = primeBefore;
        final var stopwatch = Stopwatch.createStarted();
        primeBefore = primeBefore.mod(BigInteger.TWO).equals(BigInteger.ZERO) ? primeBefore.subtract(BigInteger.ONE) : primeBefore.subtract(BigInteger.TWO);

        while (primeBefore.compareTo(BigInteger.ZERO) > 0 && !checkPrime(primeBefore)) {
          primeBefore = primeBefore.subtract(BigInteger.TWO);
        }

        final var elapsed = stopwatch.stop();

        if (primeBefore.compareTo(BigInteger.ZERO) > 0) {
          System.out.printf("First prime before %s is %s in " + elapsed + " %n", checkingFor, primeBefore);
        } else {
          System.out.printf("No previous prime found in " + elapsed + " %n");
        }
      }
      final var elapsed = stopwatchTTotal.stop();
      System.out.printf("Total time elapsed: " + elapsed + " %n");
    }
  }