给定一个正整数，编写程序计算有多少对质数的和等于这个输入的正整数，并输出结果

 1     public static void main(String[] args) {
 2         Scanner sc = new Scanner(System.in);
 3         while(true) {
 4             System.out.println("please input a positive integer: ");
 5             int n = sc.nextInt();
 6             if((n%2==1 || n==4) && isPrimer(n-2)) {
 7                 System.out.println(n+" = 2 + "+(n-2));
 8             }
 9             for(int i = 3;i <= n/2;i+=2) {
10                 if(isPrimer(i) && isPrimer(n-i)) {
11                     System.out.println(n+" = "+ i + " + "+(n-i));
12                 }
13             }
14         }    
15     }
16     public static boolean isPrimer(int n) {
17         double max = Math.sqrt(n);
18         int a = 3;
19         if(n%2 == 0)
20             return false;
21         else {
22             while(a <= max) {
23                 if(n%a == 0) {
24                     return false;
25                 }
26                 a += 2;
27             }
28         }
29         return true;
30         /*
31         for(int i = 2 ; i <= max; i++) {
32             if(n%i == 0) return false;
33         }    
34         return true;*/
35     }