Adding unknown number of nodes to a Linked list in java

Question

I have a project that ive been working on where I am using a linked list to create an integer value that has no limit to its size. It is done so by passing a String into the constructor and then each node of the linked list contains 3 digits of the number. The String values are converted to ints. Where I am struggling is iteration through the string and adding the ints to nodes correctly. Also, the number should be stored in reverse order so for example if the number is 123456 the list would have 2 nodes. Head would be 654 and the second node(tail) would be 321.

Here is my current code for the constructor

public UnboundedInt(String digits){

  head = null;//head of list
  tail = head;//tail of list
  cursor = null;//current node of list
  precursor = null;//node previous to current
  manyNodes = 0;//number of nodes in the list

  String headData;

  for(int i = 0; i < digits.length(); i ++){
     headData = digits.substring(i,i+=3);//creates substring of next 3 
        //digits
     int dataHold = Integer.parseInt(headData);//converts substring to int 
        //value
     IntNode temp = new IntNode(dataHold,null);
     temp.setLink(head);
     head = temp;
     manyNodes++;//increases number of nodes
  }
}

I am using 132456789123456789123456789 as a test value and it is currently telling me in the debug that I only have 7 nodes which are currently stored as 789 891 456 912 567 132. This should come out to be 9 nodes. Im sure theres something very trivial that I am missing but any suggestions or advice is greatly appreciated. Thank you.

Answer 1

Lets do some tracing here

132456789123456789123456789

while the substring method using i+=3 the method will be for the first loop as this

headData = digits.substring(0,3)

which means the result will be like this

loopNo     resultOfSubString    deletedDigit
1                 132                -
2                 567                4
3                 912                8
4                 456                3
5                 891                7
6                 345                2
7                 789                6
           the printed nodes

You should decrement the value of i by 1 at the end of each loop .