why Integer i = Integer.valueOf(args[0]) failed? the args[0] is a String

Question

Here is the problem description:

in my preparation for ocjp test, I have encountered a problem, and I can not figure out what's wrong with it.

package test;
class Test005{
    public static void main(String[] args){

      //Integer i = args[0];//cannot convert string to Integer
        Integer I = Integer.valueOf(args[0]); // Error ArrayOutOfBoundsException :0
        int j = 12;
        System.out.println(j == i);

    }
}

the first Integer I = args[0] is wrong, because the args[0] is a string, while the I is a int; however, the second Ineteger I = Integer.valueOf(args[0]) complies smoothly, but the JVM throw an error, and I just cannot figure it why?

If you got the ArrayOutOfBoundsException like mentioned in your code, you don't start the programm with an argument — Markus, Mar 10 '17 at 07:52
I suggest you read the [Java Tutorials](https://docs.oracle.com/javase/tutorial/). — MC Emperor, Mar 10 '17 at 07:53
Did you set arguments when run this class ? For example 'java Test005 2' — Vugar Suleymanov, Mar 10 '17 at 07:54
1) Make sure that you're effectively passing a string in the arguments (print `args.length`!) 2) Make sure that it is indeed a string representation of an integer — Oneiros, Mar 10 '17 at 08:01

arpit garg · Answer 1 · 2017-03-10T07:57:13.237

0

To run this you have to pass arguments while running the program which will be assigned to args[0], then your program will work fine. If you are using an IDE like eclipse you can pass arguments through Arguments tab. Check below link to see how you can pass arguments in eclipse IDE : http://www.cs.colostate.edu/helpdocs/eclipseCommLineArgs.html

edited Mar 10 '17 at 07:57

answered Mar 10 '17 at 07:54

arpit garg

61
5

@Scary I can't post comment as of now, so I gave an answer which I modified before you downvoted it. – arpit garg Mar 10 '17 at 08:01
thankyou, the url really help me, and I am going to learn the command line in eclipse now – qiwen li Mar 10 '17 at 08:05

score 0 · Answer 2 · answered Mar 10 '17 at 08:07

JVM throws ArrayOutOfBoundsException because your args is empty which mean you didn't pass any arguments when running this program. Try to run this command: java Test005 45. By the way, I think you should check some more cases for example: args[0] is not a number format ("ab", "a1") or when args is empty.

score 0 · Answer 3 · answered Mar 10 '17 at 09:05

The big issue you are not spotting is the fact that

Integer I = Integer.valueOf(args[0]);

will work if and only if:

args array hat AT LEAST ONE element

AND

args[0] is something you can convert into an Integer object

in your case the fisrt condition is never met, so you are trying to get the 1st element of an empty array, therfore the Exception

you didnt mention how are you testing that, are you calling that method from another class/how, or are you starting the app from a terminal/how...

why Integer i = Integer.valueOf(args[0]) failed? the args[0] is a String

3 Answers3