判斷一個數是否為質數的JAVA代碼

package math;

import java.util.Scanner;

public class Zhishupanduan {

public static void main(String[] args) {
System.out.println("請輸入一個大於等於4的整數");
Scanner sc = new Scanner(System.in);
int Q = sc.nextInt();
double X = Math.sqrt(Q);
// System.out.println(X);
int Y = (int) Math.floor(X);
// System.out.println(Y);

int sum = 0;
int num = 0;
int Z = Y * Y;
int n = 2;
int no = 0;
for (n = 2; n < Y + 2; n++) {
// System.out.println(n);

for (int i = 0; i < Q / 2; i++) {

num = n + i;
sum = n * num;
// System.out.println(n);

if (n * n <= Q & sum > Q & Z <= n * n & no == 0) {

System.out.println(+Q + "是質數");
break;
}

if (sum == Q) {
System.out.println(+Q + "不是質數" + Q + "=" + n + "*" + num);
no = 1;
break;
}

}
}

}

}