How do you check whether the given no is prime or not in java?

Answer 1

Use Euclid's algorithm to find the greatest common factor. This algorithm is much simpler to program than the method taught in school (the method that involves finding prime factors). If the greatest common factor is 1, the numbers are relatively prime.

Answer 2

package javaapplication1;

public class JavaApplication1 {

public static boolean is_prime(int val){

if (val<0) val*=-1;

if (val<2) return false;

if (val%2==0) return val==2;

int max = (int)Math.sqrt(val)+1;

for (int div=3; div<max; ++div)

if (val%div==0)

return false;

return true;

}

public static int next_prime(int val) {

do {

++val;

} while (!(is_prime(val)));

return val;

}

public static int prev_prime(int val) {

do {

--val;

} while (!(is_prime(val)));

return val;

}

public static void main(String[] args) {

System.out.print ("List of primes from -50 to 50:\n");

for (int i=-50; i<=50; ++i){

if (is_prime(i)) {

System.out.print (i);

System.out.print (" is prime\n");

}

}

System.out.print ("The next prime after -42 is ");

System.out.println (next_prime(-42));

System.out.print ("The previous prime before -42 is ");

System.out.println (prev_prime(-42));

}

}