java get the number of array values

Question

I already have the following code

public class Qn3
{
    static BigDecimal[] accbal= new BigDecimal[20];
    private static Integer[] accnums = new Integer[5];

    public static void main(String[] args)
    {
         int count;
         accnums = {1,2} //i cant add this line of code as well, what is wrong?
         while(accnums.length < 5)
         {
              count = accnums.number_of_filled_up_indexes 
               //this is not actual code i know 
           //do this as the number of values in the array are less than 5
           break;
          }
           //do this as number of values in the array are more than 5
    }
}

I must use this code there is no changing this is a requirment, so please dont suggest to use arraylist and such (i am aware of other array types and methods)

The problem is that as I have already declared that accnums must contain only 5 values, that is predefined.

I am trying to perform a check whether the ones that are not null and if all are null. To do this I have tried this but this is giving me 5 p(pre-defined integer array value not what I want).

Answer 1

public static void main(String[] args)
{
    int count = 0;
    accnums = new Integer[] {1,2,null,null,null};
    for (int index = 0; index < accnums.length; index++) 
    {
        if(accnums[index] != null)
        {
            count++;
        }
    }

    System.out.println("You have used " + count + " slots);

}

Answer 2

Try this...

accnums[0] = new Integer(1);
accnums[1] = new Integer(2);

Both the below will work if done during Declaration and Initializing time of and array.

Integer[] arr = new Integer[]{1,2,3};
Integer[] arr = {1,2,3}

But when you just declare the array as

Integer[] arr = new Integer[3]; // Still array holds no Object Reference Variable

then later initialize it this way...

arr = new Integer{1,2,3,};  // At this time it hold the ORV

Array are always initialized whether used at class or method scope , so for an int array all the values will be set to default as 0, and for Integer it will be null , as its an Wrapper object .

Eg:

    Integer[] arr = new Integer[5];

    arr[0] = 1;
    arr[1] = 2;

    System.out.println(arr.length);

    for (Integer i : arr){

        if (i!=null){

            count++;

      }



    }

    System.out.println("Total Index with Non Null Count :"+count);

}

Answer 3

accnums[0] = 1;
accnums[1] = 2;
final int count = accnums.length
    - Collections.frequency(Arrays.asList(accnums), null);
System.out.println("You have used " + count + " slots");

or, if you really must do it manually...

int count;
for (final Integer val : accnums) {
  if (val != null) {
    ++count;
  }
}