一个偶数总能表示为两个素数之和（do）

public void even(int num) {    int j = 0, num2 = 0, flag = 0, tag = 0, temp = 0;    for (int i = 3; i <= num/2; i++) {        j = (int) Math.sqrt(i);        for (int k = 2; k <= j; k++) {            if (i % k == 0) {                flag = 1;            }        }        if (flag == 0) {            num2 = num - i;            temp = (int) Math.sqrt(num2);            for (int k = 2; k <= temp; k++) {                if (num2 % k == 0) {                    tag = 1;                }            }            if (tag == 0 && num2 >= 3) {                System.out.println(num + "=" + i + "+" + num2);            }            tag = 0;        }        flag = 0;    }}