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;
}
}