无法在intellij中读取命令行参数，java？

Question

I am trying to to simply read the input of a user in my program.

import java.util.ArrayList;
import java.util.Scanner;

public class My_Counter {

public static void main (String[] args){

    Scanner my_scan = new Scanner(System.in);

    System.out.println("waiting for your number: \n");

    int num2 = my_scan.nextInt();

    System.out.println(num2);
}
}

Then I go to Run -» Edit Configurations -» and add in field "program arguments" one number. And then when I press run configuration, the program just returns:

waiting for your numbers: 

I have checked in the web already, but I cannot find anyone having the issue as me, it seemed that it has to work like this?? Or am I missing something? I am using the IDE on the newest Ubuntu version.

Answer 1

Command line arguments are stored as Strings in the String[] args array of your main method.

You're not accessing the array but instead open up a Scanner which reads userinputs from the console during runtime . Also Scanner#nextInt is a blocking operation. Which means the program is 'suspended' until an input occurs from the underlying InputStream ( System.in / stdin in this case).

In short: You've not accessed command line arguments but rather user input.

Try to input any number between Integer.MIN_VALUE and Integer.MAX_VALUE after the "waiting for your number" prompt and it will echo the entered value.

To achiev your intended implementation you can go with something as follows:

public static void main( String[] args )
{
  System.out.println( Integer.parseInt( args[0] ) );
}

Answer 2

If you want to read the number from the command line arguments, eg, when you run java -jar <my-class-compiled>.jar 15 or in your IDE (in order to pass the number 15 to your program) you will have to retrieve that number like this:

public static void main(String[] args) {
   String numberAsString = args[0]; // Will be "15"
   try {
        int number = Integer.parseInt(numberAsString);
   } catch (Exception e) { // Manage a possible exception
        System.out.println("The argument is not a valid Integer");
   }
   // Do your stuff...
}

In the other hand, if you want to pass a number on execution time, like a prompt, you will have to use Scanner.nextInt , ie: https://www.tutorialspoint.com/java/util/scanner_nextint.htm