求给定个数的质数之和

前几天去一家公司，看到一道面试题：求给定个数的质数之和，如F(3)=2+3+5=10，自己测试的代码如下

public class Test {
    
    /**
     * @Description Get after a specified number of the first prime Numbers
     * @param num a specified number
     * @return int
     * @throws
     */
    public int getAfterSpecifiedNumOfTheFirstPrimeNum(int num) {
        int beginNum = num;
        if (beginNum == 0) {
            beginNum = 1;
        }
        for (int i = (beginNum + 1);; i++) {
            if (isPrimeNum(i)) {
                return i;
            }
        }
    }
    
    /**
     * @Description 判断一个数是否为质数
     * @param num
     * @return boolean
     * @throws
     */
    private boolean isPrimeNum(int num) {
        if (num < 2) {
            return false;
        }
        for (int i = 1; i < num; i++) {
            if (num % i == 0 && i != 1) {
                return false;
            }
        }
        return true;
    }
    
    /**
     * @Description 求指定个数质数的和
     * @param num
     * @return int
     */
    public int getContPrimeNum(int num) {
        int sum = 0;
        int primeNum = 0;
        for (int i = 0; i < num; i++) {
            primeNum = getAfterSpecifiedNumOfTheFirstPrimeNum(primeNum);
            sum += primeNum;
        }
        return sum;
    }
    
    public static void main(String[] args) {
        Test t = new Test();
        System.out.println(t.getContPrimeNum(7));
    }
}