Confused about error:Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Main.main(Main.java:25)

Question

I know questions about this error have been asked before but my situation is different from all the other ones. I am writing code that comes up with the mean, variance, and standard deviation of a data set. I don't get any errors when compiling the code but when I try to run the code I get an error like this : Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Main.main(Main.java:25)

/**   
 * Main class of the Java program. 
 * 
 */

public class Main {

    public static void main(String[] args) {
        int sum = 0;
        double xBar = 0;
        double [] dataSet = {1,2,3,4}; // add data here
        int xLenght = dataSet.length;
        double [] diffrenceSquared={};
        double devSum = 0;
        double variance = 0;
        double standardDeviation = 0;
         for (double n: dataSet)
         {
            sum += n;    
         }
          xBar = sum/xLenght;

          for (int i=0; i<dataSet.length; i++)
          {
            diffrenceSquared[i] = (xBar-dataSet[i])*(xBar-dataSet[i]);
          } 
          for (double n:dataSet)
        {
              devSum += n;
        }    
        variance = devSum/xLenght;

        standardDeviation = java.lang.Math.sqrt(variance);
        System.out.println("x bar ="+xBar);
        System.out.println("variance ="+ variance);
        System.out.println("Standard Deviation ="+ standardDeviation);
    }
}

Please help me!

I suggest you to use a List if you want to add items dinamycally otherwise follow the answers. — Eric Martinez, May 27 '15 at 20:35
possible duplicate of [What causes a java.lang.ArrayIndexOutOfBoundsException and how do I prevent it?](http://stackoverflow.com/questions/5554734/what-causes-a-java-lang-arrayindexoutofboundsexception-and-how-do-i-prevent-it) — Ben N, May 27 '15 at 20:51

score 2 · Answer 1 · answered May 27 '15 at 20:34

You have declared diffrenceSquared to be a zero-length array with this declaration:

double [] diffrenceSquared={};

That means that there are no elements to assign, and every index is out of bounds.

You're attempting to assign elements to diffrenceSquared in a loop bounded by dataSet's length, so instead declare it to be that length.

double[] diffrenceSquared = new double[dataSet.length];

Eric Leibenguth · Answer 2 · 2015-05-27T20:35:08.883

0

double [] diffrenceSquared = new double[dataSet.length];

In Java, arrays are not resizable, so you have to give them the right size from the start.

Alternatively, you can use Lists, which are more flexible.

edited May 27 '15 at 20:35

answered May 27 '15 at 20:33

Eric Leibenguth

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An explanation of why this is the fix might be helpful :) – CubeJockey May 27 '15 at 20:34

Confused about error:Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0 at Main.main(Main.java:25)

2 Answers2