Addition in a linked list

Question

Hi,
I want to add numbers in a linked list. For example when i pass in the string 123456789, i reverse it so that it appears as 987654321 in the linked list. If i add this to the string 954 which appears as 459 in the linked list, i am supposed to get 123457743 but i get 1743. How do i rectify this from my code.
import java.util.LinkedList;
import java.util.ListIterator;
public class LargeInteger {
/** Constructs a new LargeInteger object from the specified String.
* The String parameter will contain the digits comprising the number
* to be represented by this LargeInteger object. The number may be
* either positive or negative, so be sure to check for a sign.
* You should throw an IllegalArgumentException if the string which is
* passed in does not contain a valid number. An invalid String would
* be one which contains any character other than a digit (however the
* first character may be a negative sign).
* @param value A String representing the number to be represented.
&nbs! p; * @throws IllegalArgumentException This exception is thrown if the
* parameter doesn't contain a valid number.
LinkedList digits = new LinkedList();
public LargeInteger(String value) throws IllegalArgumentException {
//Declare variables
boolean neg = false;
int num = 0;
int start = 0;
char ch = ' ';
Integer tempObj = new Integer(num);
//If the first character is not a - sign or it is less than the character 0
//or it is greater than the character zero, then throw
//IllegalArgumentException
//else add digits into linked list as integers
if(value.startsWith("-")) {
neg = true;
start = 1;
} else if ( !Character.isDigit(value.charAt(0)) ) {
throw new IllegalArgumentException();
for (int j = value.length()-1; j >= start; j--) {
ch = value.charAt(j);
if (Character.isDigit(ch)) {
num = Character.getNumericValue(ch);
tempObj = new Integer(num);
digits.add(tempObj);
} else {
throw new IllegalArgumentException();
} // end Constructor
public static void main(String[] args) {
LargeInteger a = new LargeInteger("954");
LargeInteger b = new LargeInteger("123456789");
LargeInteger c = a.plus(b);
System.out.println( c.toString() );
System.out.println( a.toString() );
System.out.println( b.toString() );
/** Calculates the sum of this LargeInteger object with the one passed
* as a parameter.
* @param other The number to add to the current value.
* @return The sum of this LargeInteger and the value passed as a
* parameter.
public LargeInteger plus(LargeInteger other) {
     int i = 0;
LargeInteger result = new LargeInteger("0");
int carry = 0;
ListIterator onfiltered = digits.listIterator();
ListIterator two = other.digits.listIterator();
//Add digits in linked list
for (; i < digits.size() && i < other.digits.size(); i++) {
result.digits.addFirst(
new Integer(
(((Integer) digits.get(i)).intValue()
+ ((Integer) other.digits.get(i)).intValue()
+ carry)
% 10));
carry =
(((Integer) digits.get(i)).intValue()
+ ((Integer) other.digits.get(i)).intValue()
+ carry)
/ 10;
onfiltered.next();
two.next();
//Append any remaining digits from this value to the result's
//left
for(; i < digits.size();i++){
     result.digits.addFirst(new Integer((((Integer)digits.get(i)).intValue() + carry) % 10));
     carry = (((Integer)digits.get(i)).intValue() + carry) / 10;
     onfiltered.next();
//Append any remaining digits from the other value to the result's
//left
for(; i < digits.size();i++){
     result.digits.addFirst(new Integer((((Integer)other.digits.get(i)).intValue() + carry) % 10));
     carry = (((Integer)other.digits.get(i)).intValue() + carry) / 10;
     two.next();
if(carry != 0){
     result.digits.addFirst(new Integer(carry));
return result;
} // end plus

Answer 1

Use a debugger.
Or put in some debugging statements.