Printing Arrays/Reverse Array

Question

So I have a question regarding printing arrays. These methods receive data from an array created from a file. The output should be 10 integers long in every row for as many integers are contained in the file. Let's say that the file contains {0, 1, 2, 3, 4, 5}, the output should be:

0   1   2   3   4   5

The first method works completely fine. The second method returns an error which I'll include down below. Can anyone help me figure out what's wrong? I've tried googling it but still don't understand. Here's the code:

public static void printArray(int[] array){
            System.out.println("Printing array: ");
            for (int i = 1; i<array.length+1; i++){
                    System.out.printf("%7d", array[i-1]);
                    if (i%10==0){
                            System.out.println();
                    }

            }
            System.out.println();
}
public static void reverseArray(int[] array){
            System.out.println("Printing reversed array: ");
            int a=0;
            for (int i = array.length; i>-1; i--){
                    System.out.printf("%7d", array[i]);
                    a++;
                    if (a%10==0){
                            System.out.println();
                    }
            }
            System.out.println();
}

Here's the error:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5
    at Paniagua_ArrayProcessing.reverseArray(Paniagua_ArrayProcessing.java:49)
    at Paniagua_ArrayProcessing.main(Paniagua_ArrayProcessing.java:8)

Thanks for any help! Hopefully it's only a simple problem.

Edit: This is in java btw.

Array indices start at 0 and end at this array's length minus 1; this is why you have this error. You should change your loop to `for (int i = array.length - 1; i >= 0; i--)` — fge, Mar 16 '14 at 19:14
@fge nevermind, that works! Thanks a lot :) If it was an answer I'd mark it correct lol. — a12b23c34, Mar 16 '14 at 19:18

score 3 · Accepted Answer · answered Mar 16 '14 at 19:20

3

An array goes from 0 to length-1. Change your code to:

for (int i = array.length-1; i>-1; i--){

And the code will work.

You can read more about this here: Java Language Basics: Arrays

answered Mar 16 '14 at 19:20

durron597

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score 3 · Answer 2 · answered Mar 16 '14 at 19:24

An array starts at index 0 and ends with array.length - 1. Thats the reason why you get an ArrayIndexOutOfBoundsException during access of array.length' entry of the array (which is one behind the last entry.

public static void printArray(int[] array){
    System.out.println("Printing array: ");
    for (int i = 0; i < array.length; i++){
        System.out.printf("%7d", array[i]);
        if (i % 10 == 0){
            System.out.println();
        }
    }
    System.out.println();
}

Futhermore your check for the 10th entry in the reverse array print is not correct, a was reset every time.

public static void reverseArray(int[] array){
    System.out.println("Printing reversed array: ");
    for (int i = array.length - 1; i >= 0; i--){
        System.out.printf("%7d", array[i]);
        if ((array.length - i) % 10 == 0){
            System.out.println();
        }
    }
    System.out.println();
}

score 0 · Answer 3 · answered Mar 17 '14 at 10:51

Ah this is a simple thing use :

public class reversearray {

    public static void main(String args[]){

        int arr[]={10,20,30,20,40,50};
        int size=arr.length;
        **for(int i=size-1;i>=0;i--)**{         //This is the imp change
            System.out.println(arr[i]);


        }


    }
}

score 0 · Answer 4 · answered Jun 11 '17 at 08:53

change array.length to array.length-1 because last index of array is length-1

  public static void reverseArray(int[] array){
        System.out.println("Printing reversed array: ");
        int a=0;
        for (int i = array.length-1; i>=0; i--){
                System.out.printf("%7d", array[i]);
                a++;
                if (a%10==0){
                        System.out.println();
                }
        }
        System.out.println();
  }

Printing Arrays/Reverse Array

4 Answers4