P.java

public class P {
    static boolean p(long a){
	if(a<2)return false;
	long i = 2;
	for(;i*i<=a;i+=2){
	    if(a%i==0)return false;
	    if(i<5)i--;
	}
	return true;
    }
}

Prime.java

public class Prime {
   public static boolean isPrime(long num){
	if(num<2)return false;
	long i = 2;
	while(i*i<=num){
	    if(num%i==0)return false;
	    i+=2;
	    if(i<5)i--;
	}
	return true;
    }
}