Why is not working with no args input in java

Question

I wanted to write wc program in java so wrote this code It works well when I write the command in cmd but when I don't write anything for args it should be work for all of them but it wouldn't work and give me an Exception with args[0].equal ... . Thank you for your helps!

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        int linesNumber = 0;
        int wordsNumber = 0;
        int charsNumber = 0;
        String line;
        String word;
        while (!(line = scan.nextLine()).isEmpty()) {
            linesNumber++;
            Scanner reader = new Scanner(line); //reading lines
            while (reader.hasNext()) {
                word = reader.next();
                wordsNumber++;
                charsNumber += word.length();
            }
        }
        if(args[0].isEmpty()){
            System.out.print(linesNumber +" " +wordsNumber +" " +charsNumber);
        }else if(args[0].equals("-l") || args[0].equals("--lines")){
            System.out.println(linesNumber);
        }else if(args[0].equals("-w") || args[0].equals("--words")){
            System.out.println(wordsNumber);
        }else if(args[0].equals("-c") || args[0].equals("--chars")){
            System.out.println(charsNumber);
        }
    }
}

@Berger No, args[0] is not null, it simply doesn't exist because size of array is 0 so there is no first element (indexed by 0). OP need to check for array length, not for null. — Pshemo
– Pshemo, Commented Mar 2, 2018 at 9:57
@OP When there are no arguments provided then args array is simply empty like String[] args = {}; so there are no elements in there, not even first one (indexed as 0). Before trying to access element at specified index (like [0]), you need to make sure that such element exist. Valid indexes are in range 0..length-1, otherwise you will see exception about incorrect bounds. — Pshemo
– Pshemo, Commented Mar 2, 2018 at 10:04

khelwood · Accepted Answer · 2018-03-02 09:57:41Z

3

I believe that where you have

if(args[0].isEmpty())

you mean

if (args.length==0)

If you pass no arguments to the program, args will be an empty array, so trying to access args[0] at all will raise an exception.

answered Mar 2, 2018 at 9:57

khelwood

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