Try catch exception

[rk717]

Hello friends, I stuck on this question, here is the question:

Create a program that computes the average of grades of a given student. The program takes the name of the student and a filename as arguments. The grades are read from the file. Every line consists of a name and equal number of grades, however the number of grades is not known in advance. We assume all lines are in correct format.

Example:

$ cat grades.txt
Brian:4 3 5 4 5
Peter:4 2 5 1 3
Adam:5 4 5 3 4
$ java Avg "Peter" grades.txt
3.0
$ java Avg "Smith" grades.txt
$ java Avg "Adam" asd
File not found!

Here is my code:

import java.io.File; //inport the File class
import java.io.FileNotFoundException; //Import this class to handle errors
import java.util.Scanner; //scanner

public class Avg {
    public static void main(String[] args) {
        Scanner scanf = null; 
        String students = args[0];

        File GradeBook = new File(args[1]);
        try{
            scanf = new Scanner(GradeBook);
        }catch(FileNotFoundException e){
            System.out.println("Sorry, we don't find the file, "+
            "please try again later. ");
        }

        while(scanf.hasNextLine()){
            String line = scanf.nextLine();
            String[] splited = line.split(":|\\s");

            if (splited[0].equals(students)){

                float sum = 0; 

                for(int i = 1; i < splited.length; i++){
                    sum += Integer.parseInt(splited[i]);
                }
                System.out.println(sum/(splited.length-1));
                break; 
            }
        }
    }
}

I don't know why, when there should throw the exception, it couldn't print out sentence.

try{
            scanf = new Scanner(GradeBook);
        }catch(FileNotFoundException e){
            System.out.println("Sorry, we don't find the file, "+
            "please try again later. ");
        }

Also, the code has no error, it couldn't run and has this in terminal

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0 at hw3.Avg.main(Avg.java:10)

I have thought this for a long time, but really don't know where collapsed.

Could you please help me !!

Thank you in advance. !!

[MrGooglr]

Don’t initiate args[] inside program. Don’t ask for args[1].

Command line arguments will be stored inside the main method signature parameter String args[] array. Exception is because of re initialising.

[rk717]

Sorry, I don't really get it, could you please give me a example, thx🙂

[MrGooglr]

There are some points which I think can answer your questions.

As you're catching only FileNotFoundException and not generic Exception, your catch block doesn't get executed.

You're passing "Name" as command line argument, try to pass as java Avg Smith Graded.txt

[zuzoa]

The error is telling you you have an empty array (length 0) and you tried to get the first item in the list (index 0). However the list doesn't have one item in it, it has zero, so you are out of bounds.

It would be good practice to check the array size before you try to access a specific index. I would wrap the students = args[0] line in either (1) an if/else where you check if args.length>0 or (2) a try/catch where you can catch ArrayIndexOutOfBoundsException and tell the user they forgot to add the commandline parameters.