Can someone explain me how this is working it is checking prime numbers?

Question

package javaapplication5;

import java.util.Scanner;

/**
*
* @author faakeer
*/
public class JavaApplication5 {

/**
* @param args the command line arguments
*/
;public static void main(String[] args) {
// TODO code application logic here
Scanner Scan = new Scanner(System.in);
int prime = 0;
while (true) {
System.out.println("Please enter a number");
prime = Scan.nextInt();
boolean isprime = true;
for (int x = 2; x < (prime - 1); x++) {
if ((prime % x) == 0) {
isprime = false;
}
}
if (isprime) {
System.out.println("It is a prime");
} else {
System.out.println("It is not a prime");
}
}
}

}

Answer 1

Simple logic. Using module(%) operator to see if it is prime or not.

If input is 11,
11%2 = 1
11%3 = 2
11%4 = 3
11%5 = 1
11%6 = 5
11%7 = 4
11%8 = 3
11%9 = 2
11%10 = 1
There is no "0" result so it is a prime number.

But you don't need to check some numbers. To improve performance, you can edit loop condition like this:
for(int x=2; x<=(prime/2); x++)

Also you should use "break;" to cut loop when you saw "0" result.
if((prime%x)==0){
isprime=false;
break;
}

Answer 2

Thanks but in this coding prime numbers can find easily can someone explain the mechanism plz

Answer 3

Thanks for clarifying

Answer 4

It is asking you to enter a number. (n)

There is a boolean variable(isprime) that storing result. Assigned "true" at the beginning. Assuming the number is prime.

Starting a loop to check all numbers between 2 to (n-1). If one of them divides the number(n) perfectly (if remaining is 0), then it is not a prime. So assigning false to the result variable.

After loop ended, checking the result variable(isprime) and printing a text.

This code is simple but you lose performance when you tried high numbers. There are better ways to find prime numbers.