Hello, I am struggling with this method in my Java program that deals with DNA. This is in the class CharNode.java. I have attached the CharNode class and the previous methods that I have written so far that are also part of the assignment.

// File: CharNode.java from the package edu.colorado.nodes

// Complete documentation is available from the CharNode link in:

// http://www.cs.colorado.edu/~main/docs

//package edu.colorado.nodes;

/******************************************************************************

* A CharNode provides a node for a linked list with

* char data in each node.

*

* @note

* Lists of nodes can be made of any length, limited only by the amount of

* free memory in the heap. But beyond Integer.MAX_VALUE (2,147,483,647),

* the answer from listLength is incorrect because of arithmetic

* overflow.

*

* @see

*

* Java Source Code for this class

* (www.cs.colorado.edu/~main/edu/coloradoodes/CharNode.java)

*

* @author Michael Main

* (main@colorado.edu)

*

* @version

* March 6, 2002

*

* @see Node

* @see BooleanNode

* @see ByteNode

* @see DoubleNode

* @see FloatNode

* @see IntNode

* @see LongNode

* @see ShortNode

******************************************************************************/

public class CharNode

{

// Invariant of the CharNode class:

// 1. The node's char data is in the instance variable data.

// 2. For the final node of a list, the link part is null.

// Otherwise, the link part is a reference to the

// next node of the list.

private char data;

private CharNode link;

/**

* Initialize a node with a specified initial data and link to the next

* node. Note that the initialLink may be the null reference,

* which indicates that the new node has nothing after it.

* @param initialData

* the initial data of this new node

* @param initialLink

* a reference to the node after this new node--this reference may be null

* to indicate that there is no node after this new node.

* @postcondition

* This node contains the specified data and link to the next node.

**/

public CharNode(char initialData, CharNode initialLink)

{

data = initialData;

link = initialLink;

}

/**

* Modification method to add a new node after this node.

* @param item

* the data to place in the new node

* @postcondition

* A new node has been created and placed after this node.

* The data for the new node is item. Any other nodes

* that used to be after this node are now after the new node.

* @exception OutOfMemoryError

* Indicates that there is insufficient memory for a new

* CharNode.

**/

public void addNodeAfter(char item)

{

link = new CharNode(item, link);

}

/**

* Accessor method to get the data from this node.

* @param - none

* @return

* the data from this node

**/

public char getData( )

{

return data;

}

/**

* Accessor method to get a reference to the next node after this node.

* @param - none

* @return

* a reference to the node after this node (or the null reference if there

* is nothing after this node)

**/

public CharNode getLink( )

{

return link;

}

/**

* Copy a list.

* @param source

* the head of a linked list that will be copied (which may be

* an empty list in where source is null)

* @return

* The method has made a copy of the linked list starting at

* source. The return value is the head reference for the

* copy.

* @exception OutOfMemoryError

* Indicates that there is insufficient memory for the new list.

**/

public static CharNode listCopy(CharNode source)

{

CharNode copyHead;

CharNode copyTail;

// Handle the special case of the empty list.

if (source == null)

return null;

// Make the first node for the newly created list.

copyHead = new CharNode(source.data, null);

copyTail = copyHead;

// Make the rest of the nodes for the newly created list.

while (source.link != null)

{

source = source.link;

copyTail.addNodeAfter(source.data);

copyTail = copyTail.link;

}

// Return the head reference for the new list.

return copyHead;

}

/**

* Copy a list, returning both a head and tail reference for the copy.

* @param source

* the head of a linked list that will be copied (which may be

* an empty list in where source is null)

* @return

* The method has made a copy of the linked list starting at

* source. The return value is an

* array where the [0] element is a head reference for the copy and the [1]

* element is a tail reference for the copy.

* @exception OutOfMemoryError

* Indicates that there is insufficient memory for the new list.

**/

public static CharNode[ ] listCopyWithTail(CharNode source)

{

CharNode copyHead;

CharNode copyTail;

CharNode[ ] answer = new CharNode[2];

// Handle the special case of the empty list.

if (source == null)

return answer; // The answer has two null references .

// Make the first node for the newly created list.

copyHead = new CharNode(source.data, null);

copyTail = copyHead;

// Make the rest of the nodes for the newly created list.

while (source.link != null)

{

source = source.link;

copyTail.addNodeAfter(source.data);

copyTail = copyTail.link;

}

// Return the head and tail references.

answer[0] = copyHead;

answer[1] = copyTail;

return answer;

}

/**

* Compute the number of nodes in a linked list.

* @param head

* the head reference for a linked list (which may be an empty list

* with a null head)

* @return

* the number of nodes in the list with the given head

* @note

* A wrong answer occurs for lists longer than Int.MAX_VALUE.

**/

public static int listLength(CharNode head)

{

CharNode cursor;

int answer;

answer = 0;

for (cursor = head; cursor != null; cursor = cursor.link)

answer++;

return answer;

}

/**

* Copy part of a list, providing a head and tail reference for the new copy.

* @param start/end

* references to two nodes of a linked list

* @param copyHead/copyTail

* the method sets these to refer to the head and tail node of the new

* list that is created

* @precondition

* start and end are non-null references to nodes

* on the same linked list,

* with the start node at or before the end node.

* @return

* The method has made a copy of the part of a linked list, from the

* specified start node to the specified end node. The return value is an

* array where the [0] component is a head reference for the copy and the

* [1] component is a tail reference for the copy.

* @exception IllegalArgumentException

* Indicates that start and end are not references

* to nodes on the same list.

* @exception NullPointerException

* Indicates that start is null.

* @exception OutOfMemoryError

* Indicates that there is insufficient memory for the new list.

**/

public static CharNode[ ] listPart(CharNode start, CharNode end)

{

CharNode copyHead;

CharNode copyTail;

CharNode cursor;

CharNode[ ] answer = new CharNode[2];

// Make the first node for the newly created list. Notice that this will

// cause a NullPointerException if start is null.

copyHead = new CharNode(start.data, null);

copyTail = copyHead;

cursor = start;

// Make the rest of the nodes for the newly created list.

while (cursor != end)

{

cursor = cursor.link;

if (cursor == null)

throw new IllegalArgumentException

("end node was not found on the list");

copyTail.addNodeAfter(cursor.data);

copyTail = copyTail.link;

}

// Return the head and tail references

answer[0] = copyHead;

answer[1] = copyTail;

return answer;

}

/**

* Find a node at a specified position in a linked list.

* @param head

* the head reference for a linked list (which may be an empty list in

* which case the head is null)

* @param position

* a node number

* @precondition

* position > 0.

* @return

* The return value is a reference to the node at the specified position in

* the list. (The head node is position 1, the next node is position 2, and

* so on.) If there is no such position (because the list is too short),

* then the null reference is returned.

* @exception IllegalArgumentException

* Indicates that position is not positive.

**/

public static CharNode listPosition(CharNode head, int position)

{

CharNode cursor;

int i;

if (position

throw new IllegalArgumentException("position is not positive");

cursor = head;

for (i = 1; (i

cursor = cursor.link;

return cursor;

}

/**

* Search for a particular piece of data in a linked list.

* @param head

* the head reference for a linked list (which may be an empty list in

* which case the head is null)

* @param target

* a piece of data to search for

* @return

* The return value is a reference to the first node that contains the

* specified target. If there is no such node, the null reference is

* returned.

**/

public static CharNode listSearch(CharNode head, char target)

{

CharNode cursor;

for (cursor = head; cursor != null; cursor = cursor.link)

if (target == cursor.data)

return cursor;

return null;

}

/**

* Modification method to remove the node after this node.

* @param - none

* @precondition

* This node must not be the tail node of the list.

* @postcondition

* The node after this node has been removed from the linked list.

* If there were further nodes after that one, they are still

* present on the list.

* @exception NullPointerException

* Indicates that this was the tail node of the list, so there is nothing

* after it to remove.

**/

public void removeNodeAfter( )

{

link = link.link;

}

/**

* Modification method to set the data in this node.

* @param newData

* the new data to place in this node

* @postcondition

* The data of this node has been set to newData.

**/

public void setData(char newData)

{

data = newData;

}

/**

* Modification method to set the link to the next node after this node.

* @param newLink

* a reference to the node that should appear after this node in the linked

* list (or the null reference if there is no node after this node)

* @postcondition

* The link to the node after this node has been set to newLink.

* Any other node (that used to be in this link) is no longer connected to

* this node.

**/

public void setLink(CharNode newLink)

{

link = newLink;

}

//***********************************************************************************

// START OF MY METHODS:

// toString() method

public String toString () {

CharNode cursor;

String result = "";

for (cursor = this; cursor != null; cursor = cursor.link) {

result = result + cursor.data;

} // end for loop

return result;

} // end toString method

// stringToList method

public static CharNode stringToList (String userDNA) {

if (userDNA == null) {

return null;

} // end if

char head;

head = userDNA.charAt(0);

CharNode temp = new CharNode (head, null);

CharNode tail = temp;

for (int i = 1; i

char b = userDNA.charAt(i);

tail.addNodeAfter(b);

tail = tail.getLink();

} // end for

return temp;

} // end stringToList method

// dnaToRNA Method

public static CharNode dnaToRNA (CharNode dnaList) {

if (dnaList == null) {

return null;

} // end if

String dnaString = dnaList.toString();

CharNode dnaListUpper = stringToList(dnaString.toUpperCase());

CharNode mrnaList = new CharNode(dnaListUpper.getData(), null);

CharNode temp = mrnaList;

CharNode cursor;

if (dnaListUpper.getData() == 'C') {

mrnaList.setData('G');

} // end if

else if (dnaListUpper.getData() == 'T') {

mrnaList.setData('A');

} // end else if

else if (dnaListUpper.getData() == 'G') {

mrnaList.setData('C');

} // end else if

else if (dnaListUpper.getData() == 'A') {

mrnaList.setData('U');

} // end else if

CharNode beforeCursor = mrnaList;

for (cursor = dnaListUpper.getLink(); cursor != null; cursor = cursor.getLink()) {

if (cursor.getData() == 'C') {

temp = new CharNode('G', null);

} // end if

else if (cursor.getData() == 'T') {

temp = new CharNode('A', null);

} // end else if

else if (cursor.getData() == 'G') {

temp = new CharNode ('C', null);

} // end else if

else if (cursor.getData() == 'A') {

temp = new CharNode ('U', null);

} // end else if

beforeCursor.setLink(temp);

beforeCursor = temp;

} // end for loop

return mrnaList;

} // end dnaToRNA Method

} // end class

Task 4: Write a method called subSequence that given two linked lists of characters determines whether the shorter list (let us call it S) is a subsequence of the longer list (let us call it L). If the shorter list is a subsequence of the longer list, then the method should return the length of the shortest segment in L that contains Sas a subsequence. For example, for sequences CAT and ACAGTGCGTATAT from the above example, the method should return 4 If the shorter list is not a subsequence of the longer list, then the method should return value -1 The method should have two parameters (of type CharNode) - heads of the two linked lists It is not known in advance which of the parameters (the first one or the second one) contains a shorter list. The length of the lists must be checked first to determine which of the two given lists is (Note: The goal of this task is to practice working with linked lists. Converting lists into strings and using String methods is not permitted.) In your program you should prompt the user to enter two strings, convert the strings into linked lists using the method which you wrote before (to convert a String into a linked list of characters), call the method to determine whether a shorter list is a subsequence ofa longer list and output the result