Thread: ArrayIndexOutOfBoundsException

Hi,

I have this code which is meant to reverse the array a, however I get a message ArrayIndexOutOfBoundsException - why is this, and how do I correct the code to not get this problem?

public class MirrorElements {
    /**
     * Reverse the array a
     * Error message: ArrayIndexOutOfBoundsException
     * @param args
     */
     public static void main (String[] args) {
         int i = 0;
         while (i < a.length /2) {
             int original = a[i]; // swap a[i] and a[a.length - i]
             a[i] = a[a.length - i];
             a[i.length - i] = original;
             i = i + 1;
         }
     }
 
}

Originally Posted by NightFire91

Hi,

I have this code which is meant to reverse the array a, however I get a message ArrayIndexOutOfBoundsException - why is this, and how do I correct the code to not get this problem?

you get an ArrayIndexOutOfBoundsException because the index of an array is zero-based and the length field of the array is not zero-based. so if you want to get the last char in the array you must use a[length - 1]. here is the corrected code:

public class MirrorElements {
 
	public static void main(String[] args) {
		char[] a = { 'h', 'a', 'l', 'l','o',' ', 'w','o', 'r','l','d'};
		StringBuilder sf = new StringBuilder(new String(a));
 
		int i = 0;
		while (i < a.length / 2) {
			int original = a[i]; // store a[i] before swapping
			// swap a[i] with length - i -1
			a[i] = a[a.length - i -1];
			// store the original char
			a[a.length - i -1] = (char)original;
			i = i + 1;
		}
		System.out.println(a);
		// the StringBuffer has a reverse() method, so
		// use it to check if your a[] is the same
		System.out.println(sf.reverse());
	}
}

i use a literal of chars for my example but you can change easily to your param. and i used the StringBuilder only for testing purpose. good luck.