Hey I can't seem to get my code to work, there is something wrong with the constructor and I just can't figure out what it is. I had it working for the constructor and tried it for some of the methods but even then it still gave me NullPointerException
import java.util.NoSuchElementException;
public class LinkedString
{
//Required Nodes/counters to track positions in LinkedList
private Node start;
private Node end;
private int counter;
private int i = 0;
//Inner class Node provides the node object required to create links
private class Node
{
public char data;
public Node next;
}
//This constructor allows the user to input a array of characters
//and have them created into a LinkedString object
public LinkedString(char[] value)
{
start.data = value[0];
counter = 0;
for(int i = 0 ; i < value.length ; i++)
{
if ( start == null)
{
start.data = value[i];
start.next = end;
counter++;
}
else
{
Node newNode = new Node();
newNode.data = value[i];
end.next = newNode;
newNode.next = null;
end = newNode;
counter++;
}
}
}
//This constructor allows the user to input a String
//getting each character and creating it into a LinkedString object
public LinkedString(String value)
{
counter=0;
for(int i = 0; i < value.length(); i++)
{
if(start == null)
{
start.data = value.charAt(i);
start.next = end;
counter++;
}
else
{
Node newNode = new Node();
newNode.data=value.charAt(i);
end.next = newNode;
newNode.next = null;
end = newNode;
}
}
}
//This accessor returns a value at the specified index
//The 1st character has an index of 0 and will throw
//a no such element exception if there is no char @ given index
public char charAt(int index)
{
Node current = start;
boolean found = false;
char temp = 0;
int i = 0;
while (current.next != null && i <= index)
{
current = current.next;
if(i == index)
{
found = true;
//Return done, and Data is wrong Edit.
}
i++;
temp = current.data;
}
if(found == false) {
throw new NoSuchElementException();
}
return temp;
}
//concat connects two linkedString objects together and updates the
//counter for how many chars are in the combined list
public LinkedString concat(LinkedString value)
{
end.next = value.start;
end = value.end;
counter = counter + value.length();
return value;
}
//isEmpty checks to see if the list has a initial value
//if it doesnt its empty and returns true
public boolean isEmpty()
{
if(start == null)
{
return true;
}
else
{
return false;
}
}
//length() returns the counter variable which counts the number of
// characters in the linked string
public int length()
{
return counter;
}
//substring returns a copy of the linked string from a specified point
//to another, if the user attempts to copy a value from a not existing
//index point it throws NoSuchElementException
public Node substring(int startIndex, int endIndex)
{
Node current = start;
Node sIndex;
Node eIndex;
Node copy = null;
int i = 0;
while(current.next != null && i <= startIndex)
{
current = current.next;
if(i == startIndex)
{
sIndex = current;
sIndex.next = copy;
while(current.next != null && i <= endIndex)
{
current = current.next;
copy.next = current;
copy = current;
if(i == endIndex)
{
eIndex = current;
eIndex.next = null;
copy.next = eIndex;
}
i++;
}
if(i < endIndex)
throw new NoSuchElementException();
}
i++;
}
return copy;
}
}
public class LinkedStringMain {
public static void main(String[] args) {
LinkedString linked = new LinkedString("stack");
System.out.println(" " + linked.charAt(0));
System.out.println(" " + linked.isEmpty());
}
}
