Problem 3 (List Implementation) (35 points): Write a method in the DoublyLList c

Question

 Problem 3 (List Implementation) (35 points): Write a method in the DoublyLList class that deletes the first item containing a given value from a doubly linked list. The header of the method is as follows: public boolean removeValue(T aValue) where T is the general type of the objects in the list and the methods returns true if such an item is found and deleted. Include testing of the method in a main method of the DoublyLList class.  ------------------------------------------------------------------------------------- /**    A doubly-linked implementation of the ADT list.     @author Frank M. Carrano    @author Joseph Erickson    @version 4.0  */ public class DoublyLList<T> implements ListInterface<T> {         private Node firstNode; // Reference to first node         private int  numberOfEntries;          public DoublyLList()         {                 initializeDataFields();         } // end default constructor          public final void clear() // Note the final method         {                 initializeDataFields();         } // end clear          public void add(T newEntry)                             // OutOfMemoryError possible         {                 Node newNode = new Node(newEntry);                  if (isEmpty())                         firstNode = newNode;                 else                                                            // Add to end of non-empty list                 {                         Node lastNode = getNodeAt(numberOfEntries);                         lastNode.setNextNode(newNode);  // Make last node reference new node                         newNode.setPreviousNode(lastNode);                 } // end else                  numberOfEntries++;         }  // end add          public void add(int newPosition, T newEntry) // OutOfMemoryError possible         {                 if ((newPosition >= 1) && (newPosition <= numberOfEntries + 1))                 {                         Node newNode = new Node(newEntry);                          if (newPosition == 1)                           // Case 1                         {                                 newNode.setNextNode(firstNode);                                 if (firstNode != null)                          // List is not empty                                         firstNode.setPreviousNode(newNode);                                 firstNode = newNode;                         } // end if                         else                                                            // Case 2: List is not empty                         {                                                                       // and newPosition > 1                                 Node nodeBefore = getNodeAt(newPosition - 1);                                 Node nodeAfter = nodeBefore.getNextNode();                                 newNode.setNextNode(nodeAfter);                                 newNode.setPreviousNode(nodeBefore);                                 nodeBefore.setNextNode(newNode);                                 if (nodeAfter != null)                  // not the last element                                         nodeAfter.setPreviousNode(newNode);                         } // end else                          numberOfEntries++;                 } // end if                 else                         throw new IndexOutOfBoundsException("Illegal position given to add operation.");         } // end add          public T remove(int givenPosition)         {                 T result = null;                                                        // Return value                  if ((givenPosition >= 1) && (givenPosition <= numberOfEntries))                 {                         assert !isEmpty();                          if (givenPosition == 1)                                 // Case 1: Remove first entry                         {                                 result = firstNode.getData();           // Save entry to be removed                                 firstNode = firstNode.getNextNode();                                 firstNode.setPreviousNode(null);                         } // end if                         else                                                                    // Case 2: Not first entry                         {                                 ///////////////////////////////////////////                                 // INSERT YOUR CODE HERE                                                                                                                                    ///////////////////////////////////////////                         } // end else                          numberOfEntries--;                         return result;                 } // end if                 else                         throw new IndexOutOfBoundsException("Illegal position given to remove operation.");         } // end remove          public T replace(int givenPosition, T newEntry)         {                 if ((givenPosition >= 1) && (givenPosition <= numberOfEntries))                 {                            assert !isEmpty();                          Node desiredNode = getNodeAt(givenPosition);                         T originalEntry = desiredNode.getData();                         desiredNode.setData(newEntry);                         return originalEntry;                 } // end if                 else                         throw new IndexOutOfBoundsException("Illegal position given to replace operation.");         } // end replace          public T getEntry(int givenPosition)         {                 if ((givenPosition >= 1) && (givenPosition <= numberOfEntries))                 {                         assert !isEmpty();                         return getNodeAt(givenPosition).getData();                 } // end if                 else                         throw new IndexOutOfBoundsException("Illegal position given to getEntry operation.");         } // end getEntry          public boolean contains(T anEntry)         {                 boolean found = false;                 Node currentNode = firstNode;                  while (!found && (currentNode != null))                 {                         if (anEntry.equals(currentNode.getData()))                                 found = true;                         else                                 currentNode = currentNode.getNextNode();                 } // end while                  return found;         } // end contains          public int getLength()         {                 return numberOfEntries;         } // end getLength          public boolean isEmpty()         {                 boolean result;                  if (numberOfEntries == 0) // Or getLength() == 0                 {                         assert firstNode == null;                         result = true;                 } // end if                 else                 {                         assert firstNode != null;                         result = false;                 } // end else                  return result;         } // end isEmpty          public T[] toArray()         {                 // The cast is safe because the new array contains null entries                 @SuppressWarnings("unchecked")                 T[] result = (T[])new Object[numberOfEntries];  // Unchecked cast                  int index = 0;                 Node currentNode = firstNode;                 while ((index < numberOfEntries) && (currentNode != null))                 {                         result[index] = currentNode.getData();                         currentNode = currentNode.getNextNode();                         index++;                 } // end while                          return result;         } // end toArray          // Initializes the class's data fields to indicate an empty list.         private void initializeDataFields()         {                 firstNode = null;                 numberOfEntries = 0;         } // end initializeDataFields          // Returns a reference to the node at a given position.         // Precondition: List is not empty;         //               1 <= givenPosition <= numberOfEntries         private Node getNodeAt(int givenPosition)         {                 assert !isEmpty() && (1 <= givenPosition) && (givenPosition <= numberOfEntries);                 Node currentNode = firstNode;                  // Traverse the chain to locate the desired node                 // (skipped if givenPosition is 1)                 for (int counter = 1; counter < givenPosition; counter++)                         currentNode = currentNode.getNextNode();                  assert currentNode != null;                  return currentNode;         } // end getNodeAt          private class Node         {                 private T    data;              // Entry in list                 private Node next;              // Link to next node                 private Node previous;  // Link to previous node                  private Node(T dataPortion)                 {                         data = dataPortion;                         next = null;                         previous = null;                 } // end constructor                  private Node(T dataPortion, Node nextNode)                 {                         data = dataPortion;                         next = nextNode;                         previous = null;                 } // end constructor                  private T getData()                 {                         return data;                 } // end getData                  private void setData(T newData)                 {                         data = newData;                 } // end setData                  private Node getNextNode()                 {                         return next;                 } // end getNextNode                  private void setNextNode(Node nextNode)                 {                         next = nextNode;                 } // end setNextNode                  private Node getPreviousNode()                 {                         return previous;                 } // end getPreviousNode                  private void setPreviousNode(Node previousNode)                 {                         previous = previousNode;                 } // end setPreviousNode         } // end Node } // end DoublyLList 

     ------------------------------------------------------------------------------------------- /** An interface for the ADT list.     Entries in a list have positions that begin with 1.      @author Frank M. Carrano     @author Timothy M. Henry     @version 4.0 */ public interface ListInterface<T> {    /** Adds a new entry to the end of this list.        Entries currently in the list are unaffected.        The list's size is increased by 1.        @param newEntry  The object to be added as a new entry. */    public void add(T newEntry);        /** Adds a new entry at a specified position within this list.        Entries originally at and above the specified position        are at the next higher position within the list.        The list's size is increased by 1.        @param newPosition  An integer that specifies the desired                            position of the new entry.        @param newEntry     The object to be added as a new entry.        @throws  IndexOutOfBoundsException if either                 newPosition < 1 or newPosition > getLength() + 1. */    public void add(int newPosition, T newEntry);        /** Removes the entry at a given position from this list.        Entries originally at positions higher than the given        position are at the next lower position within the list,        and the list's size is decreased by 1.        @param givenPosition  An integer that indicates the position of                              the entry to be removed.        @return  A reference to the removed entry.        @throws  IndexOutOfBoundsException if either                  givenPosition < 1 or givenPosition > getLength(). */    public T remove(int givenPosition);        /** Removes all entries from this list. */    public void clear();        /** Replaces the entry at a given position in this list.        @param givenPosition  An integer that indicates the position of                              the entry to be replaced.        @param newEntry  The object that will replace the entry at the                         position givenPosition.        @return  The original entry that was replaced.        @throws  IndexOutOfBoundsException if either                 givenPosition < 1 or givenPosition > getLength(). */    public T replace(int givenPosition, T newEntry);        /** Retrieves the entry at a given position in this list.        @param givenPosition  An integer that indicates the position of                              the desired entry.        @return  A reference to the indicated entry.        @throws  IndexOutOfBoundsException if either                 givenPosition < 1 or givenPosition > getLength(). */    public T getEntry(int givenPosition);        /** Retrieves all entries that are in this list in the order in which        they occur in the list.        @return  A newly allocated array of all the entries in the list.                 If the list is empty, the returned array is empty. */    public T[] toArray();        /** Sees whether this list contains a given entry.        @param anEntry  The object that is the desired entry.        @return  True if the list contains anEntry, or false if not. */    public boolean contains(T anEntry);        /** Gets the length of this list.        @return  The integer number of entries currently in the list. */    public int getLength();            /** Sees whether this list is empty.        @return  True if the list is empty, or false if not. */    public boolean isEmpty(); } // end ListInterface 

Explanation / Answer

Java Code:

//remove method

public T remove(int givenPosition)
{
T result = null; // Return value
int currentPosition=1;
if ((givenPosition >= 1) && (givenPosition <= numberOfEntries))
{
assert !isEmpty();

if (givenPosition == 1) // Case 1: Remove first entry
{
result = firstNode.getData(); // Save entry to be removed
firstNode = firstNode.getNextNode();
firstNode.setPreviousNode(null);
} // end if
else // Case 2: Not first entry
{
///////////////////////////////////////////
// INSERT YOUR CODE HERE
Node currentNode=firstNode;
while(currentNode!=null){ //iterate through list
if(currentPosition==givenPosition){//if current position matches givenposition
result=currentNode.getData(); // save entry to be removed
Node previousOfCurrent=currentNode.getPreviousNode();//get previous node
Node nextOfCurrent=currentNode.getNextNode(); // get next node

if(previousOfCurrent!=null)
previousOfCurrent.setNextNode(nextOfCurrent); //make previous point to next of //current

else

firstNode=nextOfCurrent;
if(nextOfCurrent!=null)//if next not null make it point to previous of current
nextOfCurrent.setPreviousNode(previousOfCurrent);
  
}
currentPosition++; //iterate to next. increment position
currentNode=currentNode.getNextNode();
}
  
  
///////////////////////////////////////////
} // end else

numberOfEntries--;
return result;
} // end if
else
throw new IndexOutOfBoundsException("Illegal position given to remove operation.");
} // end remove

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