Java examples for java.lang:int prime
get Previous Prime number
//package com.java2s; import java.util.Collection; import static java.lang.Math.sqrt; public class Main { public static long getPrevPrime(long startVal) { for (long i = startVal - 1;; i--) if (isPrime(i)) return i; }/* w w w. j ava 2 s . c o m*/ public static boolean isPrime(long test) { if (test < 2) return false; if (test < 4) return true; if (test % 2 == 0) return false; if (test < 9) return true; if (test % 3 == 0) return false; long sqrt = (long) sqrt(test); long i = 5; while (i <= sqrt) if (test % (i) == 0 || test % (i + 2) == 0) return false; else i += 6; return true; } public static boolean isPrime(long test, Collection<Long> primes) { if (test < 2) return false; for (Long prime : primes) { if (prime * prime > test) return true; if (test % prime == 0) return false; } //Return false here is better than false true if collection is not big enough return false; } }