Error message: Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1

Question

I am in my first class of Java programming and one of the assignments we were given was to create a value string which displays in reverse order separated by commas. I know I am probably missing something very simple, but after hours of trying I just don't know where I am going wrong?

My code works, however I keep getting this error message:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: -1 
    at ip2_jolley.IP2_Jolley.main(IP2_Jolley.java:148) 
Three, Two, One Java Result: 1

This is the code I am using:

String[] f = {"One", "Two", "Three"};
if (f.length > 0) System.out.print (f[2]);
for (int i = 1; i < f.length; i--){
    System.out.print(", " + f[i]); 
}

It won't let me click the up arrow so I edited to thank them. — Violette
– Violette, Commented Apr 6, 2014 at 21:17

Martin Dinov · Accepted Answer · 2014-04-06 20:59:13Z

2

In your code, you start at 1, loop until the length of the array, but decrement i each time. That's a bit mixed up. What you want to do is start at the end of your array (so f.length - 1) and keep moving to the "left" of the array until you are at the beginning of it. So you want this:

for (int i = f.length-1; i >= 0; i--){
   System.out.print(f[i]); 
}

answered Apr 6, 2014 at 20:59

Martin Dinov

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3 Comments

rpax Over a year ago

It would be fine if you explain why

rpax Over a year ago

Yes. You deserve my +1

Violette Over a year ago

Thank you changing the 1 loop to a 0 fixed the missing / wrong output =)

ThomasK · Accepted Answer · 2014-04-06 21:08:34Z

1

You start your loop with int i = 1 and then reduce it by 1 every loop which will result in i being lower than 0.

Instead of using int i = 1, you probably want to use int i = f.length

Edit

What you wanted is probably this:

  String[] f = {"One", "Two", "Three","Four","Five"};

    //start at f.length - 1, continue until there is no item left
    for (int i = f.length-1; i >= 0; i--){

        //print current item
        System.out.print(f[i]);

        //if it is not the last item, print separator
        if(i>0){
            System.out.print(", ");
        }
    }
}

Edited with some explanation

edited Apr 6, 2014 at 21:08

answered Apr 6, 2014 at 20:58

ThomasK

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Comments

user3504561 · Accepted Answer · 2014-04-06 20:57:00Z

0

Do you mean:

for (int i = 0; i < f.length; i++)

Instead of:

for (int i = 1; i < f.length; i--)

answered Apr 6, 2014 at 20:57

user3504561

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3 Comments

Jason C Over a year ago

I did not downvote the answer, but I imagine it is because the OP specifically is trying to display the values in reverse order.

user3504561 Over a year ago

Okay I will delete my answer then.

Violette Over a year ago

Thank you =) adding the ++ to replace the -- was what I needed.

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