Design and implement a program using linked lists (using Java Collections) to cr

Question

Design and implement a program using linked lists (using Java Collections) to create, manage, and retrieve information on a self-reorganizing list of names and telephone numbers. When a node is created its ct is set to zero and it is placed at the first of the list. Every time a node is referenced, its ct is increased by 1 and when ct reaches 3 (a magic number?) the node should be deleted from its current place on the list, replaced at the head of the list, and its ct reset to 0. The program should recognize three commands, requested by the prompt CMD: A Add a phone number. The program prompts for a name, and a telephone number. L Look up a number. The program prompts the user to input a name. C Change a phone number. The program prompts with name and a new phone number, printing an error message if the name does not exist in the list. S Save the list to a file, as described below. The program should initialize itself from a text file of names and phone numbers (which contains a list of names and phone numbers that may initially be empty). When the command S is entered, the program should rewrite the file with the current form of the list. Also perform the following analysis: what is the order of magnitude to perform each operation

Explanation / Answer

import java.util.Scanner;
class Node
{
protected int data;
protected Node link;
public Node()
{
link = null;
data = 0;
}
public Node(int d,Node n)
{
data = d;
link = n;
}
public void setLink(Node n)
{
link = n;
}
public void setData(int d)
{
data = d;
}
public Node getLink()
{
return link;
}
public int getData()
{
return data;
}
}
class linkedList
{
protected Node start;
protected Node end ;
public int size ;
public linkedList()
{
start = null;
end = null;
size = 0;
}
public boolean isEmpty()
{
return start == null;
}
public int getSize()
{
return size;
}
public void insertAtStart(int val)
{
Node nptr = new Node(val, null);
size++ ;
if(start == null)
{
start = nptr;
end = start;
}
else
{
nptr.setLink(start);
start = nptr;
}
}
public void insertAtEnd(int val)
{
Node nptr = new Node(val,null);
size++ ;
if(start == null)
{
start = nptr;
end = start;
}
else
{
end.setLink(nptr);
end = nptr;
}
}
public void insertAtPos(int val , int pos)
{
Node nptr = new Node(val, null);
Node ptr = start;
pos = pos - 1 ;
for (int i = 1; i < size; i++)
{
if (i == pos)
{
Node tmp = ptr.getLink() ;
ptr.setLink(nptr);
nptr.setLink(tmp);
break;
}
ptr = ptr.getLink();
}
size++ ;
}
public void display()
{
System.out.print(" Singly Linked List = ");
if (size == 0)
{
System.out.print("empty ");
return;
}
if (start.getLink() == null)
{
System.out.println(start.getData() );
return;
}
Node ptr = start;
System.out.print(start.getData()+ "->");
ptr = start.getLink();
while (ptr.getLink() != null)
{
System.out.print(ptr.getData()+ "->");
ptr = ptr.getLink();
}
System.out.print(ptr.getData()+ " ");
}
}
public class SinglyLinkedList
{
public static void main(String[] args)
{   
Scanner scan = new Scanner(System.in);
linkedList list = new linkedList();
System.out.println("Singly Linked List Test ");
char ch;
do
{
System.out.println(" Singly Linked List Operations ");
System.out.println("1. insert at begining");
System.out.println("2. insert at end");
System.out.println("3. insert at position");
System.out.println("4. delete at position");
System.out.println("5. check empty");
System.out.println("6. get size");
int choice = scan.nextInt();
switch (choice)
{
case 1 :
System.out.println("Enter integer element to insert");
list.insertAtStart( scan.nextInt() );   
break;
case 2 :
System.out.println("Enter integer element to insert");
list.insertAtEnd( scan.nextInt() );   
break;   
case 3 :
System.out.println("Enter integer element to insert");
int num = scan.nextInt() ;
System.out.println("Enter position");
int pos = scan.nextInt() ;
if (pos <= 1 || pos > list.getSize() )
System.out.println("Invalid position ");
else
list.insertAtPos(num, pos);
break;
case 4 :
System.out.println("Enter position");
int p = scan.nextInt() ;
if (p < 1 || p > list.getSize() )
System.out.println("Invalid position ");
else
list.deleteAtPos(p);
break;
case 5 :
System.out.println("Empty status = "+ list.isEmpty());
break;   
case 6 :
System.out.println("Size = "+ list.getSize() +" ");
break;   
default :
System.out.println("Wrong Entry ");
break;   
}
list.display();
System.out.println(" Do you want to continue (Type y or n) ");
ch = scan.next().charAt(0);
} while (ch == 'Y'|| ch == 'y');   
}
}

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