for (int i = 0; i < array_g.length; i++){
        int largest = i;
        for (int j = largest + 1; j < array_g.length; j++) {
            if (array_g[j] > array_g[largest]) {
                largest = j;
            }
        }
        //grades
        double temp = array_g[largest];
        array_g[largest] = array_g[i];
        array_g[i] = temp;
        //Names
        String tempString = array_n[i];
        array_n[i] = array_n[largest];
        array_n[largest] = tempString;
    }

我试着把不同的年级按照他们的名字从高到低排序。