How to use arrayList sort and manipulate the vlaue

By using Java 11, I am trying to find the average value inside the ArrayList. The algorithm i want to develop is ((value inside list/maximum value)*100)/length of list). I got number format runtime error while I run the program. java.lang.NumberFormatException is the error i got.

import java.io.*;
import java.util.*;

public class Main{
    public static void main(String[] args)throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(br.readLine());
        StringTokenizer st = new StringTokenizer(br.readLine()," ");
        double[] grades = new double[N];
        
        for(int i = 0; i < N; i++){
            grades[i] = Integer.parseInt(st.nextToken());
        }
        
        double sum = 0;
        Arrays.sort(grades);
        
        for(int i = 0; i < grades.length; i++){
            sum += (grades[i]/grades[grades.length-1])*100;
        }
        System.out.println(sum/grades.length);
       
    }
}

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Answer

I find two issues with the code above:

1. The parsing of br.readLine() to int is the line which throws NumberFormatException, since br.readLine() contains both numbers and spaces (at least). Since the line is NOT a valid number, the parsing fails.

   Example:

   • User enters the following when br.readLine() is executed: “1 2 3 4”
   • The next instruction looks like: int N = Integer.parseInt("1 2 3 4")
   • The correct number should not contain spaces: “1234”

2. This one is not really a bug, however, you’re asking the user to input the numbers again on the second appearance of br.readLine here: new StringTokenizer(br.readLine()," ");

Solution

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

// REMOVE NEXT LINE
// int N = Integer.parseInt(br.readLine());

StringTokenizer st = new StringTokenizer(br.readLine()," ");

// Read the number of tokens in the string
// The input "1 2 3 4" on the example above should return 4 tokens
int N = st.countTokens();

double[] grades = new double[N];