如何从方法中正确返回值？在无效输入上接收奇数错误

Question

import java.util.Scanner; 
public class Main
{
  public static void main(String[] args)
  {
    Scanner keyboard = new Scanner(System.in);
    double score = 0, avg, sum = 0;
    int index = 0, count = 0, num = 0;

    num = readInput(keyboard, num);

    double Test[] = new double[num];
    System.out.print("\n");

    while(count < Test.length)
    {
      System.out.printf("Enter your test score #%d:", count + 1);
      try
      {
        score = keyboard.nextDouble();
      }

      catch(java.util.InputMismatchException e)
      {
        System.out.print("You have entered a non-numerical value, please try again\n");
        keyboard.next();
        continue;
      }
      if (score >= 0)
      {
        Test[count] = score;
        sum = sum + score;
      }
      else
      {
        System.out.print("You have entered an invalid grade, please try again\n");
        continue;
      }
      count++;
    }

    double maxValue = Test[0];
    for (int i = 1; i < Test.length; i++) 
    {
      if (Test[i] > maxValue) 
      {
        maxValue = Test[i];
      }
    }  

    double minValue = Test[0];
    for (int i = 1; i < Test.length; i++) 
    {
      if (Test[i] < minValue) 
      {
        minValue = Test[i];
        index = i;
      }
    }

    System.out.print("\nThe highest value is: " + maxValue + "\n");
    System.out.print("The lowest value is: " + minValue + "\n");

    avg = sum / Test.length;
    System.out.printf("Your grade average is: %.1f \n\n", avg);

    System.out.print("Would you like to drop the lowest grade: Y or N:");
    char choice = keyboard.next().charAt(0);

    if (choice == 'Y' || choice == 'y')
    {
      double newSum = sum - minValue;
      double newAvg = newSum / (Test.length - 1);

      System.out.print("\nYour old scores were: ");
      System.out.print(Test[0]);
      for (int i = 1; i < Test.length; i++) 
      { 
        System.out.print(", " + Test[i]);
      }

      System.out.print("\n\nYour new scores are: ");
      for (int i = 0; i < Test.length; i++) 
      { 
        if (index != 0 && i != index)
        {
          if (i >= 1)
          {
            System.out.print(", "); 
          }  
          System.out.print(Test[i]);
        } 
        else if (i != index)
        {
          if (i >= 2)
          {
            System.out.print(", "); 
          }  
          System.out.print(Test[i]); 
        }
      }

      System.out.printf("\n\nYour new average is: %.1f\n", newAvg);
    }
    else if (choice == 'N' || choice == 'n')
    {
      System.out.print("Your average has stayed the same.\n");
      return;
    }
    else
    {
      System.out.print("You have entered an invalid response. Bye.\n");
      return;
    }

  }

  public static int readInput(Scanner keyboard, int val)
  {
    System.out.print("\nHow many scores would you like to enter:");
    val = 0;
    try
    {
      val = keyboard.nextInt();
    }

    catch(java.util.InputMismatchException e)
    {
      System.out.print("You have entered a non-numerical value.\n");
      keyboard.next();
      readInput(keyboard, val);
    }

    if (val < 0)
    {
      System.out.print("You have entered a negative value.\n");
      readInput(keyboard, val);
    }
    else if (val == 0)
    {
      System.out.print("If you have no test grades then you do not need this program.\n");
      readInput(keyboard, val);
    }
    return val;
  }
}

错误是由代码底部的函数引起的。

这是我目前的输出：

您想要输入多少分数：h 您输入了非数值。

您想要输入多少分数：8 如果您没有测试成绩，那么您不需要此程序。

您想要输入多少分数：8

线程“main”中的异常java.lang.ArrayIndexOutOfBoundsException：0     在Main.main（Main.java:53） 以非零状态退出

似乎无法识别输入的第二个值。即使我进入8，该程序认为它为零，我无法弄清楚原因。在无效输入后的第三个条目上程序崩溃。注意：如果用户在第一次尝试时输入有效值，则程序正常工作。只有当用户首先输入无效输入时才会发生此错误。

编辑：我知道错误是因为我的数组中没有值，但我在问为什么会发生这种情况。输入无效输入后，该值不会从函数返回，因此数组在空时尝试运行。