Question

Please help me ONLY for the second method : public static int[] runningGroups(String[] inputFileNames) throws IOException.

The second method has an "array of files as a parameter". and return int [ ]. Each element of the return array is the number of group that can get from the first method.   

I got an error Exception in thread "main" java.lang.NullPointerException

Here my code:

import java.io.*;
import java.util.ArrayList;
import java.util.Scanner;

public class RunningGroups {

public static void main(String[] args) throws IOException {
  String file = args[0];

  System.out.print(" Total : ");
  System.out.print(runningGroups(file));

            String[] test = new String[5];
            String t1 = args[1] ;
            String t2 = args[2] ;
            String t3 = args[3] ;
            String t4 = args[4];
          
           test[0] = t1;
           test[1] = t2;
           test[2] = t3;
           test[3] = t4;
          
          int[] result = new int[test.length];
          result = runningGroups(test);
           System.out.println("Test array");
           for(int i=0; i<result.length; i++){
              System.out.print(result[i] + " ");
           }

        }

public static int runningGroups(String inputFileName) throws IOException{
    Scanner input = new Scanner(new File(inputFileName));
  String str = "";
  while(input.hasNext()) {
   str = str + input.next() + " ";
  }

  String[] temp = str.split(" ");
  int n = Integer.parseInt(temp[0]);
  int[] start = new int[n];
     int[] speed = new int[n];
     int l = 0,k = 0;
    
     ArrayList<Integer> min_speed_pos = new ArrayList<Integer>();
     int j = 0;
     int min_speed = 1000000;    
    
     for(int i = 1; i<temp.length; i = i+2) {
     start[l] = Integer.parseInt(temp[i]);
     l++;
     }
    
     for(int i = 2; i<temp.length; i= i+2) {   
     speed[k] = Integer.parseInt(temp[i]);
     min_speed = Math.min(min_speed, speed[k]);
     k++;
     }
      
       for(int i = 0; i<n; i++){
          if(speed[i] == min_speed)
             min_speed_pos.add(i);
       }
       return min_speed_pos.size();
       }

public static int[] runningGroups(String[] inputFileName) throws IOException{
int[] groups = new int[inputFileName.length];
  
               for(int i =0; i< inputFileName.length; i++){
                  String temp = inputFileName[i];
                  groups[i] = runningGroups(temp);
               }
  
               
   return groups;
          }
}

Args List: 1in *2.in *3.in *4.in *5.in 6.in 7.in *8.in *9.in 10.in Max Points: 5 Extra credits Description: Create a program named RunningGroups.java and implements the following static method: ubli this method returns the number of running groups tat public static int it returns an int array, each element in the array represents the number of running groups for its corresponding input file s(str inputFileNames) thrONS IOException Then test your program Here is the problem description: There are N (1 < N <= 200,000) people running on a single-lane track. Assuming the track is infinitely long. Each person starts at a distinct position on the track, and runners may run at different speeds. Runners cannot pass each other because there is only one lane in the track. When a faster runner catches up to another person, he or she must slow down to avoid running into the other people, becoming part of the same running group. Eventually, no more runners will run into each other and all runners will run in a group (it is possible there is only one runner in a group), Peter wonders h。ฟ many running groups will be formed eventually. Peter has been working on this problem for more than 3 hours and feels frustrated at this point. Please help this poor guy find this number Input data: The first line of the input file contains the integer N, followed by N lines containing the starting position(>=e) and speed (>0) of each runner. Both numbers(starting position and speed) are at most 1 billion. All runners start at different positions, and these(starting position) will be given in increasing order in the input SANPLE INPUT: 1 2 6 1 The number of running group: 2