I want to declare an empty array in Java and then I want do update it but the code is not working

You are creating an array of zero length (no slots to put anything in)

 int array[]={/*nothing in here = array with no slots*/};

and then trying to assign values to array slots (which you don’t have, because there are none)

array[i] = number; //array[i] = element i in the array of length 0

You need to define a larger array to fit your needs

 int array[] = new int[4]; //Create an array with 4 elements [0],[1],[2] and [3] each containing an int value