How to check command arguments in main class java

Question

i've got the following program: i have a jar file which is getting 4 parameteres from main method :input file,order by, sort direction, output file. The input file is the file where information will be read , order by is sorting by (test,runs , etc), sort direction (asc, desc) and outputfile where information will be saved. Here is my code in main method :

      if (args.length > 0)
        {
            if (args[0].isEmpty())
            {
                System.out.println("Enter input file");
                System.exit(1);
            }
            else
            {
                args[0] = inputFile;
            }
            if (args[1].isEmpty())
            {
                System.out.println("Enter order by");
                System.exit(1);
            }
            else
            {
                args[1] = orderBy;
            }
            if (args[2].isEmpty())
            {
                System.out.println("Enter sort direction");
                System.exit(1);
            }
            else
            {
                args[2] = sortDirection;
            }
            if (args[3].isEmpty())
            {
                System.out.println("Enter output file");
                System.exit(1);
            }
            else
            {
                args[3] = outputFile;
            }

        }
        else
        {
            System.out.println("Must enter parameteres!");
            System.exit(0);
        }

          SaveInfoManager.SaveInFile(inputFile, sortDirection, orderBy, outputFile);

And i have a following error: ArraysIndexOutOfBoundsException when i do not enter some argument. Example i do not enter the 3rd argument which is sort direction and i want to print message that is not entered. But i do not understand why is throwing that exception even i make a check. Can you tell me where is my fault and how i can do it properly ?

The args array has the size of the number of provided arguments. You'd better check the size of the array to know how many were provided. — Arnaud
– Arnaud, Commented Aug 16, 2018 at 7:32
You checked if args.length > 0 before accessing any args. That tells you args[0] is within bounds, but that's all. You can't safely access args[1] without checking args.length > 1, or args[2] without checking args.length > 2, etc. — Kevin Anderson
– Kevin Anderson, Commented Aug 16, 2018 at 7:34

Turamarth · Accepted Answer · 2018-08-16 07:34:30Z

1

args[n].isEmpty() checks whether the string that is contained in position n of the array is empty, which results in ArraysIndexOutOfBoundsException if the array has less than n elements.
In order to check the length of the array you need to use

if(args.length == 4){ ... }

answered Aug 16, 2018 at 7:34

Turamarth

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2 Comments

George Over a year ago

Ok, but how i can check the specific 2nd parameter for example. And tell the user it must be filled

Turamarth Over a year ago

@George You could use if(args.length<2)... to see if there are less than 2 parameters. Checking if a specific parameter is missing isn't really possible since you only use the order of the arguments to indicate which one is which. If you want to check specific parameters I suggest that you add flags to the arguments.

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