Question

Using Java create a program that does the following: Modify the LinkedList1 class by adding sort() and reverse() methods. The reverse method reverses the order of the elements in the list, and the sort method rearranges the elements in the list so they are sorted in alphabetical order. Do not use recursion to implement either of these operations. Extend the graphical interface in the LinkedList1Demo class to support sort and reverse commands, and use it to test the new methods. This should have two separate source files. LinkedList1 Class and LinkedList1Demo.

Include these modifications:

• Read in the names from an input file.
• Instead of using a graphical interface, create a menu method and use it to interface with the user.
• Include menu options to add, remove and find names as well as to sort and reverse the entire contents of the list.
• The program should execute until the user enters "exit."

LinkedList1 class:

/**

The LinkedList1 class implements a Linked list.

*/

class LinkedList1

{

/**

The Node class stores a list element

and a reference to the next node.

*/

  

private class Node

{

String value;   

Node next;

  

/**

Constructor.

@param val The element to store in the node.

@param n The reference to the successor node.

*/

  

Node(String val, Node n)

{

value = val;

next = n;

}

  

/**

Constructor.

@param val The element to store in the node.

*/

  

Node(String val)

{

// Call the other (sister) constructor.

this(val, null);

}

}   

private Node first; // list head

private Node last; // last element in list

/**

Constructor.

*/

  

public LinkedList1()

{

first = null;

last = null;

}

  

/**

The isEmpty method checks to see

if the list is empty.

@return true if list is empty,

false otherwise.

*/

  

public boolean isEmpty()

{

return first == null;   

}

  

/**

The size method returns the length of the list.

@return The number of elements in the list.

*/

  

public int size()

{

int count = 0;

Node p = first;   

while (p != null)

{

// There is an element at p

count ++;

p = p.next;

}

return count;

}

  

/**

The add method adds an element to

the end of the list.

@param e The value to add to the

end of the list.   

*/

  

public void add(String e)

{

if (isEmpty())

{

first = new Node(e);

last = first;

}

else

{

// Add to end of existing list

last.next = new Node(e);

last = last.next;

}

}

  

/**

The add method adds an element at a position.

@param e The element to add to the list.

@param index The position at which to add

the element.

@exception IndexOutOfBoundsException When

index is out of bounds.

*/

  

public void add(int index, String e)

{

if (index < 0 || index > size())

{

String message = String.valueOf(index);

throw new IndexOutOfBoundsException(message);

}

// Index is at least 0

if (index == 0)

{

// New element goes at beginning

first = new Node(e, first);

if (last == null)

last = first;

return;

}

// Set a reference pred to point to the node that

// will be the predecessor of the new node

Node pred = first;

for (int k = 1; k <= index - 1; k++)

{

pred = pred.next;   

}

// Splice in a node containing the new element

pred.next = new Node(e, pred.next);

// Is there a new last element ?

if (pred.next.next == null)

last = pred.next;   

}

  

/**

The toString method computes the string

representation of the list.

@return The string form of the list.

*/

  

public String toString()

{

StringBuilder strBuilder = new StringBuilder();

  

// Use p to walk down the linked list

Node p = first;

while (p != null)

{

strBuilder.append(p.value + "\n");

p = p.next;

}

return strBuilder.toString();

}

  

/**

The remove method removes the element at an index.

@param index The index of the element to remove.

@return The element removed.

@exception IndexOutOfBoundsException When index is

out of bounds.   

*/

  

public String remove(int index)

{

if (index < 0 || index >= size())

{

String message = String.valueOf(index);

throw new IndexOutOfBoundsException(message);

}

String element; // The element to return   

if (index == 0)

{

// Removal of first item in the list

element = first.value;

first = first.next;

if (first == null)

last = null;   

}

else

{

// To remove an element other than the first,

// find the predecessor of the element to

// be removed.

Node pred = first;

  

// Move pred forward index - 1 times

for (int k = 1; k <= index -1; k++)

pred = pred.next;

  

// Store the value to return

element = pred.next.value;

  

// Route link around the node to be removed

pred.next = pred.next.next;

  

// Check if pred is now last

if (pred.next == null)

last = pred;

}

return element;

}

  

/**

The remove method removes an element.

@param element The element to remove.

@return true if the remove succeeded,

false otherwise.

*/

  

public boolean remove(String element)

{

if (isEmpty())

return false;

  

if (element.equals(first.value))

{

// Removal of first item in the list

first = first.next;

if (first == null)

last = null;   

return true;

}

  

// Find the predecessor of the element to remove

Node pred = first;

while (pred.next != null &&

!pred.next.value.equals(element))

{

pred = pred.next;

}

// pred.next == null OR pred.next.value is element

if (pred.next == null)

return false;

  

// pred.next.value is element

pred.next = pred.next.next;

  

// Check if pred is now last

if (pred.next == null)

last = pred;

  

return true;   

}

  

public static void main(String [] args)

{

LinkedList1 ll = new LinkedList1();

ll.add("Amy");

ll.add("Bob");

ll.add(0, "Al");

ll.add(2, "Beth");

ll.add(4, "Carol");

System.out.println("The members of the list are:");

System.out.print(ll);

}

}

Program Output:

The members of the list are:

Al

Amy

Beth

Bob

Carol

Answer 1

// LinkedList1.java
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

/**

The LinkedList1 class implements a Linked list.

*/
public class LinkedList1 {
  
   /**

   The Node class stores a list element

   and a reference to the next node.

   */

     
   private class Node

   {

   String value;   

   Node next;

  

   /**

   Constructor.

   @param val The element to store in the node.

   @param n The reference to the successor node.

   */

  

   Node(String val, Node n)

   {

   value = val;

   next = n;

   }

  

   /**

   Constructor.

   @param val The element to store in the node.

   */

  

   Node(String val)

   {

   // Call the other (sister) constructor.

   this(val, null);

   }

   }   

   private Node first; // list head

   private Node last; // last element in list

   /**

   Constructor.

   */

  

   public LinkedList1()

   {

   first = null;

   last = null;

   }

  

   /**

   The isEmpty method checks to see

   if the list is empty.

   @return true if list is empty,

   false otherwise.

   */

  

   public boolean isEmpty()

   {

   return first == null;   

   }

  

   /**

   The size method returns the length of the list.

   @return The number of elements in the list.

   */

  

   public int size()

   {

   int count = 0;

   Node p = first;   

   while (p != null)

   {

   // There is an element at p

   count ++;

   p = p.next;

   }

   return count;

   }

  

   /**

   The add method adds an element to

   the end of the list.

   @param e The value to add to the

   end of the list.   

   */

  

   public void add(String e)

   {

   if (isEmpty())

   {

   first = new Node(e);

   last = first;

   }

   else

   {

   // Add to end of existing list

   last.next = new Node(e);

   last = last.next;

   }

   }

  

   /**

   The add method adds an element at a position.

   @param e The element to add to the list.

   @param index The position at which to add

   the element.

   @exception IndexOutOfBoundsException When

   index is out of bounds.

   */

  

   public void add(int index, String e)

   {

   if (index < 0 || index > size())

   {

   String message = String.valueOf(index);

   throw new IndexOutOfBoundsException(message);

   }

   // Index is at least 0

   if (index == 0)

   {

   // New element goes at beginning

   first = new Node(e, first);

   if (last == null)

   last = first;

   return;

   }

   // Set a reference pred to point to the node that

   // will be the predecessor of the new node

   Node pred = first;

   for (int k = 1; k <= index - 1; k++)

   {

   pred = pred.next;   

   }

   // Splice in a node containing the new element

   pred.next = new Node(e, pred.next);

   // Is there a new last element ?

   if (pred.next.next == null)

   last = pred.next;   

   }

  

   /**

   The toString method computes the string

   representation of the list.

   @return The string form of the list.

   */

  

   public String toString()

   {

   StringBuilder strBuilder = new StringBuilder();

  

   // Use p to walk down the linked list

   Node p = first;

   while (p != null)

   {

   strBuilder.append(p.value + "\n");

   p = p.next;

   }

   return strBuilder.toString();

   }

  

   /**

   The remove method removes the element at an index.

   @param index The index of the element to remove.

   @return The element removed.

   @exception IndexOutOfBoundsException When index is

   out of bounds.   

   */

  

   public String remove(int index)

   {

   if (index < 0 || index >= size())

   {

   String message = String.valueOf(index);

   throw new IndexOutOfBoundsException(message);

   }

   String element; // The element to return   

   if (index == 0)

   {

   // Removal of first item in the list

   element = first.value;

   first = first.next;

   if (first == null)

   last = null;   

   }

   else

   {

   // To remove an element other than the first,

   // find the predecessor of the element to

   // be removed.

   Node pred = first;

  

   // Move pred forward index - 1 times

   for (int k = 1; k <= index -1; k++)

   pred = pred.next;

  

   // Store the value to return

   element = pred.next.value;

  

   // Route link around the node to be removed

   pred.next = pred.next.next;

  

   // Check if pred is now last

   if (pred.next == null)

   last = pred;

   }

   return element;

   }

  

   /**

   The remove method removes an element.

   @param element The element to remove.

   @return true if the remove succeeded,

   false otherwise.

   */

  

   public boolean remove(String element)

   {

   if (isEmpty())

   return false;

  

   if (element.equals(first.value))

   {

   // Removal of first item in the list

   first = first.next;

   if (first == null)

   last = null;   

   return true;

   }

  

   // Find the predecessor of the element to remove

   Node pred = first;

   while (pred.next != null &&

   !pred.next.value.equals(element))

   {

   pred = pred.next;

   }

   // pred.next == null OR pred.next.value is element

   if (pred.next == null)

   return false;

  

   // pred.next.value is element

   pred.next = pred.next.next;

  

   // Check if pred is now last

   if (pred.next == null)

   last = pred;

  

   return true;   

   }
  
   public void sort()
   {
       if(first != null && first.next != null)
       {
           Node curr;
           boolean swapped = true;
           while(swapped)
           {
               curr = first;
               swapped = false;
              
               while(curr.next != null)
               {
                   if(curr.value.compareTo(curr.next.value) > 0)
                   {
                       String data = curr.value;
                       curr.value = curr.next.value;
                       curr.next.value = data;
                       swapped = true;
                   }
                  
                   curr = curr.next;
               }
           }
          
           curr = first;
           while(curr.next != null)
               curr = curr.next;
           last = curr;
       }
   }
  
   public void reverse()
   {
       if(first != null && first.next != null)
       {
           Node curr = first;
           first = null;
           while(curr != null)
           {
               Node save = curr;
               curr = curr.next;
               save.next = first;
               first = save;
           }
          
           curr = first;
           while(curr.next != null)
               curr = curr.next;
           last = curr;
       }
   }
  
   public boolean find(String element)
   {
       if(isEmpty())
       {
           return false;
       }else
       {
           Node curr = first;
           while(curr != null)
           {
               if(curr.value.equals(element))
                   return true;
               curr = curr.next;
           }
          
           return false;
       }
   }

   public static void main(String[] args) throws FileNotFoundException {

       LinkedList1 list = new LinkedList1();
       String filename = "names.dat";
       Scanner scan = new Scanner(new File(filename));
       String name;
      
       while(scan.hasNextLine())
       {
           name = scan.nextLine();
           list.add(name);
       }
       System.out.println(list);
       scan.close();
       scan = new Scanner(System.in);
       int choice;
      
       do
       {
           System.out.println("1. Add a name");
           System.out.println("2. Remove a name");
           System.out.println("3. Search for a name");
           System.out.println("4. Sort the list");
           System.out.println("5. Reverse the list");
           System.out.println("6. Exit");
           System.out.print("Enter your choice (1-6) : ");
           choice = scan.nextInt();
           scan.nextLine();
           if(choice == 1)
           {
               System.out.print("Enter a name : ");
               name = scan.nextLine();
               list.add(name);
               System.out.println(list);
           }else if(choice == 2)
           {
               System.out.print("Enter a name : ");
               name = scan.nextLine();
               list.remove(name);
               System.out.println(list);
           }else if(choice == 3)
           {
               System.out.print("Enter a name : ");
               name = scan.nextLine();
               if(list.find(name))
                   System.out.println(name+" found in list");
               else
                   System.out.println(name+" not found in list");
           }else if(choice == 4)
           {
               list.sort();
               System.out.println(list);
           }else if(choice == 5)
           {
               list.reverse();
               System.out.println(list);
           }else if(choice != 6)
               System.out.println("Invalid choice");
       }while(choice != 6);
      
       scan.close();
   }

}
//end of LinkedList1.java

Output:

Input file:

Output: