Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException in Finding Max Element

Question

Whenever I am trying to run this code, it gives me out of bound exception. Can anyone point me out what's wrong with it.

package com.programs.interview;
import java.util.Scanner;

public class FindMaxNumInArray {

public static void main (String[] args) 
{ 
    Scanner scan = new Scanner (System.in); 
    System.out.print("Enter the size of the array: "); 
    int arraySize = scan.nextInt(); 
    int[] myArray = new int[arraySize]; 
    System.out.print("Enter the " + arraySize + " values of the array: "); 
    for (int i = 0; i < arraySize; i++)
        myArray[i] = scan.nextInt(); 
    for (int j = 0; j < arraySize; j++) 
        System.out.println(myArray[j]); 
    System.out.println("In the array entered, the larget value is "+ maximum(myArray,arraySize) + "."); 
} 

public static int maximum(int[] arr, int Arraylength){
    int tmp;
    if (Arraylength == 0)
        return arr[Arraylength];
    tmp = maximum(arr, Arraylength -1);
    if (arr[Arraylength] > tmp)
        return arr[Arraylength];
    return tmp;
  }
}

Output

Enter the size of the array: 5 Enter the 5 values of the array: 1 2 3 4 5 1 2 3 4 5 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5 at com.programs.interview.FindMaxNumInArray.maximum(FindMaxNumInArray.java:26) at com.programs.interview.FindMaxNumInArray.main(FindMaxNumInArray.java:17)

The Console Gives me this out put: Enter the size of the array: 5 Enter the 5 values of the array: 1 2 3 4 5 1 2 3 4 5 Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 5 at com.programs.interview.FindMaxNumInArray.maximum(FindMaxNumInArray.java:26) at com.programs.interview.FindMaxNumInArray.main(FindMaxNumInArray.java:17) — Ali Ansari
– Ali Ansari, Commented Feb 22, 2014 at 21:33
Yes, because an array with 5 elements does not have a element index [5]. Only 0 1 2 3 4 — deviantfan
– deviantfan, Commented Feb 22, 2014 at 21:34
Does it have to be recursive? Using a loop would be simpler, and faster. — Peter Lawrey
– Peter Lawrey, Commented Feb 22, 2014 at 21:35
So ...? I mean is there problem in initializing the array with 5 ? — Ali Ansari
– Ali Ansari, Commented Feb 22, 2014 at 21:36
Actually m new in programming, and i was interviewed with recursive method. — Ali Ansari
– Ali Ansari, Commented Feb 22, 2014 at 21:38

Jon Skeet · Accepted Answer · 2014-02-22 22:10:50Z

3

This is the problem:

if (arr[Arraylength] > tmp)

Valid array indexes go from 0 to length-1 inclusive. array[array.length] is always invalid, and on the initial call, ArrayLength is equal to arr.length.

It's not clear why you're using recursion at all, to be honest. An iterative solution would be much simpler - but you'll need to work out what you want to do if the array is empty.

EDIT: If you really want how I would write the recursive form, it would be something like this:

/** Returns the maximum value in the array. */
private static int maximum(int[] array) {
    if (array.length == 0) {
        // You need to decide what to do here... throw an exception,
        // return some constant, whatever.
    }
    // Okay, so the length will definitely be at least 1...
    return maximumRecursive(array, array.length);
}

/** Returns the maximum value in array in the range [0, upperBoundExclusive) */
private static int maximumRecursive(int[] array, int upperBoundExclusive) {
    // We know that upperBoundExclusive cannot be lower than 1, due to the
    // way that this is called. You could add a precondition if you really
    // wanted.
    if (upperBoundExclusive == 1) {
        return array[0];
    }
    int earlierMax = maximumRecursive(array, upperBoundExclusive - 1);
    int topValue = array[upperBoundExclusive - 1];
    return Math.max(topValue, earlierMax);

    // Or if you don't want to use Math.max
    // return earlierMax > topValue ? earlierMax : topValue;
}

edited Feb 22, 2014 at 22:10

answered Feb 22, 2014 at 21:34

Jon Skeet

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8 Comments

Ali Ansari Over a year ago

You mean this would help : public static int maximum(int[] arr, int Arraylength){ int tmp; if (Arraylength == 0) return arr[Arraylength]; tmp = maximum(arr, Arraylength-1); if (arr[Arraylength-1] > tmp) return arr[Arraylength]; return tmp; }

Jon Skeet Over a year ago

@AliAnsari: No, that will still fail - you're still returning arr[Arraylength], and if the array is empty then you're still going to try to take the first element from it. Again, you really need to decide what you want to do if the length of the array is 0.

Ali Ansari Over a year ago

Thnx Alot: it worked now: public static int maximum(int[] arr, int Arraylength){ int tmp; if (Arraylength == 0) return arr[Arraylength]; tmp = maximum(arr, Arraylength-1); if (arr[Arraylength-1] > tmp) return arr[Arraylength-1]; return tmp; }

Jon Skeet Over a year ago

@AliAnsari: Well that's still not going to work if the array is empty, but other than that it's okay. It's not how I would write the code, mind you - I'd use iteration rather than recursion.

Ali Ansari Over a year ago

M also convenient with iterative solution, but my need was recursive. Kindly , can u re-write it as if you will have to write it. I need to compare that one with mine to clear that where am i mistaken.

|

Jigar Joshi · Accepted Answer · 2014-02-22 21:34:57Z

2

you can't access

arr[Arraylength]

the last element would be at

arr[Arraylength -1]

for example if you have

int arr[] = new int[5];

then the elements would be at 4, because index starts from 0

arr[0], arr[1], arr[2], arr[3], arr[4]

answered Feb 22, 2014 at 21:34

Jigar Joshi

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1 Comment

Ali Ansari Over a year ago

Thnx alot for explaining

ltalhouarne · Accepted Answer · 2014-02-22 21:36:11Z

0

Your issue is in the following piece of code:

if (arr[Arraylength] > tmp)
            return arr[Arraylength];

Indexes start at 0, so you will be out of bound for an array with 5 elements [1,2,3,4,5] indexes: [0,1,2,3,4].

answered Feb 22, 2014 at 21:36

ltalhouarne

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Comments

Peter Lawrey · Accepted Answer · 2014-02-22 21:37:30Z

0

I would use a plain loop. Java doesn't do recursion particularly well.

public static int maximum(int[] arr) {
    int max = Integer.MIN_VALUE;
    for(int i : arr) if (i > max) max = i;
    return max;
}

answered Feb 22, 2014 at 21:37

Peter Lawrey

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1 Comment

Ali Ansari Over a year ago

Actually m new in programming, and i was interviewed with recursive method.

Devavrata · Accepted Answer · 2014-02-22 21:43:55Z

0

here

System.out.println("In the array entered, the larget value is "+ maximum(myArray,arraySize) + ".");

you are passing the arraysize where in maximum method you are returning arr[Arraylength] which giving ArrayIndexOutOfBound so change either in calling maximum(yArray,arraySize-1) or return arr[Arraylength-1] statement.

answered Feb 22, 2014 at 21:43

Devavrata

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