ArrayIndexOutOfBoundsException when printing out values from an array

Question

The program should print out values stored in an array of size 5 after the user has input the values.

Here is my code:

import java.util.Scanner;

public class Arrays_Qu1 {

  public static void main(String[] args) {

    Scanner sc= new Scanner(System.in);
    int arr[]= new int [5];

    System.out.println("Enter a number");

    int i;
    for (i=0;i<arr.length;i++) {
      arr[i]=sc.nextInt();
    }

    System.out.println(arr[i]);
  }
}

After I enter the 5th value, the program does not terminate but instead throws:

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5

Debug your code and you'll see that `i` will be 5 after the loop which is out of the index bounds [0,4]. That's because the loop will increment `i` after before checking the condition, i.e. it will increment `i` to 5 and then check `i < arr.length` (i.e. `i < 5`) and terminate the loop - but `i` remains 5. — Thomas, Sep 15 '16 at 12:57
The I++ executes one more time than you're thinking; in the last iteration of the loop, right after the array[] assignment. — ABuckau, Sep 15 '16 at 12:59
@Thomas Can you show me how sequence in which this part `for (i=0;i — Tia, Sep 15 '16 at 17:36
That should be explained in any decent loop tutorial but basically it is like this: `for( init; condition; increment ) { body; }` results in a sequence like `init, condition check, body, increment, condition check, body, increment, ...` - of course the sequence ends if the condition check fails. :) — Thomas, Sep 16 '16 at 07:58

Shahid · Accepted Answer · 2016-09-15T13:04:45.133

Because you are printing outside the loop and it is trying to print arr[5] which is out of bound of the array. The print should be in loop if you want to print each element.

int i;
for (i = 0; i < arr.length; i++) {
    arr[i] = sc.nextInt();
    System.out.println(arr[i]); // to print each element
}

// value of i is now 5, so arr[i] is invalid
System.out.println(arr[i-1]); // to print last element
System.out.println(Arrays.toString(arr)); // to print whole array

score 0 · Answer 2 · answered Sep 15 '16 at 12:58

You should access the last element of the array like:

 System.out.println(arr[i - 1])

but I believe printing just the last element of an array is not what you want. So you should move line

 System.out.println(arr[i])

in a for loop and it should be ok.

ArrayIndexOutOfBoundsException when printing out values from an array

2 Answers2