Question

I would like to know to know how do i compare the arguments passed into a java main method.

eg java hello -i

I tried printing args[0] and it does indeed gives me -i. however what i want to achieve is:

if args.length == 0 {
  do something
}
else if args[0] =="-i"{
  do something
}

However i keep getting index out of bound exception. is there anyway to convert the string in the string array args to just a string type so i can compare it?

public static void main(String[] args) {
  if args.length == 0 {
    do something
  }
  else if args[0] =="-i"
    do something
  } 


}

for example if they start the program without any arguments, i will call init() method. but if they entered -i as arguments, i will call install() instead..

Answer 1

The code you’ve given wouldn’t even compile, but this does work:

public class Test {
    public static void main(String[] args) {
        if (args.length == 0) {
            System.out.println("No arguments!");
        } else if (args[0].equals("-i")) {
            System.out.println("-i passed");
        } else {
            System.out.println("Something else");
        }
    }
}

Note that it’s important that you’re using else here – this would fail, for example:

if (args.length == 0) {
    System.out.println("No arguments!");
}
if (args[0].equals("-i")) {
    System.out.println("-i passed");
}

at that point you’re checking args[0] even if the length of the array is 0. Given that you’ve given pseudo-code at the moment (no brackets round the conditions) I wonder whether that’s the problem in your real code.

(Also note the use of equals instead of == as others have already pointed out.)