java.lang.ArrayIndexOutOfBoundsException

Question

I'm a novice Java programmer. I dont know what is wrong with the main method, it keeps pointing me to this line

    int x = Integer.parseInt(args[0]);

this is my code

public static void main(String[] args) {

    assert args.length == 1;
    int x = Integer.parseInt(args[0]);
    while (x != 1) {
        x = nextInt(x);
        System.out.print(" " + x);
    }
}

public static int nextInt(int x) {
    if (x % 2 == 0) {
        return x / 2;
    } else
        return 3 * x + 1;
}

When asking about an error, please post the error message. There could be a few things going on, and the actual error is more helpful than just the line number. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Aug 1, 2013 at 2:14
@hexafraction Java doesn't do shell-style name arguments. args[0] is the first argument, not the name of the class. — chrylis -cautiouslyoptimistic-
– chrylis -cautiouslyoptimistic-, Commented Aug 1, 2013 at 2:15
Java does not behave this way (First argument is program name). Does the assert evalutate to true? — Logan Murphy
– Logan Murphy, Commented Aug 1, 2013 at 2:20
Regarding the 'compiler-errors' tag on this, ArrayIndexOutOfBoundsException is not a compilation error; it's a runtime error. — jarmod
– jarmod, Commented Aug 1, 2013 at 2:22
If not then you must define arguments to your program. Otherwise the array "args" will be size 0 and 0 will be out of bounds. — Logan Murphy
– Logan Murphy, Commented Aug 1, 2013 at 2:22

morgano · Accepted Answer · 2013-08-01 02:16:08Z

3

I'm going to assume that you are using a number in the first argument of your program call.

You are using asserts, verify that assertions are activated. Execute your code with the VM argument: -ea.

answered Aug 1, 2013 at 2:16

morgano

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3 Comments

chrylis -cautiouslyoptimistic- Over a year ago

This is good advice, but if the tag is correct, he's having compiler problems, not runtime.

morgano Over a year ago

@chrylis do you see any compiler problems in the line with trouble? it is more likely that: 1) he's doesn't have a parseable number as first argument, or 2) the doesn't even have any arguments in the command line

chrylis -cautiouslyoptimistic- Over a year ago

No, it looks perfectly correct, but it is tagged compiler-errors.

Java Devil · Accepted Answer · 2013-08-01 03:09:59Z

1

Simply said, in Java the java.lang.ArrayIndexOutOfBoundsException means there is no array element in the specified index of your array.

So make sure you input at least 1 argument when running your java app from the command prompt. In your case, it should be parsable to an Integer.

For Example:

java {class_name_with_main_methof} {argument_1} {argument_2}

edited Aug 1, 2013 at 3:09

Java Devil

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answered Aug 1, 2013 at 2:25

Dinusha Kariyawasam

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3 Comments

chrylis -cautiouslyoptimistic- Over a year ago

Exactly one, because of the assert condition.

RiaD Over a year ago

@chrylis asserts are not always on

chrylis -cautiouslyoptimistic- Over a year ago

@RiaD No, they're not, but that's what he's using for error-checking in this example. It's not the best choice, but that's another issue.

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