java如何在没有集合的情况下执行数字操作？

Question

我有一个快速的java程序来执行一些数字操作。现在它使用Collections库，但是任务要求不要使用java中的任何方法。util。收藏课。我能用什么把它关掉？现在我有一些集合对ArrayList进行排序，并得到最小值和最大值

谢谢

如果你需要我的代码：

import java.util.ArrayList;
import java.util.Scanner;
import java.util.Collections;

class Main {

  public static void main(String[] args) {
    ArrayList<Integer> grades = new ArrayList<Integer>();
    Scanner input = new Scanner(System.in);
    System.out.println("Input:");
    int i = 0;
    int strs = 0;
    strs = input.nextInt();
    while (strs != -1) {
      if(strs > 100 || strs < 0 && strs != -1) {
        strs = input.nextInt();
      }
      else {
        grades.add(strs);
        strs = input.nextInt();
        i++;
      }
    }
    System.out.println("\nOutput:\n");
    System.out.println(grades);
    System.out.println("Sorted:");
    Collections.sort(grades);
    System.out.println(grades);
    int sum = 0;
    for (int g : grades) sum += g;
    double average = sum / grades.size();
    average = 1 * sum / grades.size();
    System.out.println("Average: " + average);
    int mid = grades.size()/2; 
    double median = grades.get(mid); 
    if (grades.size()%2 == 0) { 
      median = (median + grades.get(mid-1))/2; 
    }
    System.out.println("Median: " + median);
    int max = Collections.max(grades);
    int min = Collections.min(grades);
    int range = max - min;
    System.out.println("Range: " + range);
    }
  }