请教算质数的java题！

public class Prime {
/**
* 用来计算前num个质数的和,并在控制台打印
*
* @param num
* 用来进行求和运算的质数的个数
*/
public static void sumOfPrime(int num) {
int count = num;
int j;
int sum = 0;// 最后的累计和
for (int i = 2; count != 0; i++) {
j = 2;
for (; j <= Math.sqrt(i); j++) {
if (i % j == 0) {
break;
}
}
if (j > Math.sqrt(i)) {
System.err.println("第" + (num - count + 1) + "个质数:" + i);
sum += i;
count--;
}
}
System.err.println("前" + num + "个质数的和为:" + sum);
}

public static void main(String[] args) {
sumOfPrime(20);//测试
}
}

public class Sushu
{ public static void main(String args[])
{ int i,j;
for(i=2;i<=100;i++)
{ for(j=2;j<=i/2;j++)
{
if(i%j==0)
break;