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

Question

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

public class JavaConversion
{
    public static void main(String args[])
    {
        int array[]={};
        int number = 5, i = 0,j = 0;
        while (i<4) {
            array[i]=number;
            i=i+1;
        }
        while (j<4) {
            System.out.println(array[j]);
        }
    }
}

Answer 1

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

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

and then trying to assign values to array elements (which you don't have, because there are no slots)

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

Answer 2

Your code compiles just fine. However, your array initialization line is wrong:

int array[]={};

What this does is declare an array with a size equal to the number of elements in the brackets. Since there is nothing in the brackets, you're saying the size of the array is 0 - this renders the array completely useless, since now it can't store anything.

Instead, you can either initialize the array right in your original line:

int array[] = { 5, 5, 5, 5 };

Or you can declare the size and then populate it:

int array[] = new int[4];
// ...while loop

If you don't know the size of the array ahead of time (for example, if you're reading a file and storing the contents), you should use an ArrayList instead, because that's an array that grows in size dynamically as more elements are added to it (in layman's terms).

Answer 3

You need to give the array a size:

public static void main(String args[])
{
    int array[] = new int[4];
    int number = 5, i = 0,j = 0;
    while (i<4){
        array[i]=number;
        i=i+1;
    }
    while (j<4){
        System.out.println(array[j]);
        j++;
    }
}