Question

n JAVA, students will create a linked list structure that will be used to support a role playing game. The linked list will represent the main character inventory. The setting is a main character archeologist that is traveling around the jungle in search of an ancient tomb. The user can add items in inventory by priority as they travel around (pickup, buy, find), drop items when their bag is full, and use items (eat, spend, use), view their inventory as a whole or by category, request the number of items in inventory, and request to see values for specific inventory items. The categories for items are food, coins, archeology tools, artifacts, and documents. Each item should have an item number (unique integer value in priority order), category (string or integer), a description (string), and a value (integer). The program will use the linked list structure to allow the user to do the functions mentioned above; add (beginning/end), remove (from end), insert (based on ID number), delete (based on ID number), print inventory, print inventory by category, tell if the inventory is empty, tell how many items are in inventory, tell how many items in each category, and search for an item by name or ID and return its value. The code must validate the user input for valid choices and valid input type and throw exceptions that result in an appropriate message to the user. The code must also throw exceptions for trying to retrieve/print a node from an empty list.

Use the code below to finish the rest of the code.

/**
   The LinkedList class implements a Linked list that contains inventory
*/

class LinkedList
{
/**
   The Node class stores a list element
   and a reference to the next node.
*/

private class Node
{
int id; //Item Number
String Category; //category
String Description; // Description
int value;//value
Node next;

/**
   Constructor.
   @param val The element to store in the node.
   @param n The reference to the successor node.
*/

Node(int itnum, String Catg, String Desc, int val, Node n)
{
id = itnum;
Category = Catg;
Description = Desc;
value = val;
next = n;
}

/**
   Constructor.
   @param val The element to store in the node.
   */

Node(int itnum, String Catg, String Desc, int val)
{
   // Call the other (sister) constructor.
   id = itnum;
Category = Catg;
Description = Desc;
value = val;
}
}

private Node first; // list head
private Node last; // last element in list

/**
   Constructor.
*/

public LinkedList()
{
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(int itnum, String Catg, String Desc, int val)
{
if (isEmpty())
{
first = new Node(itnum,Catg,Desc,val);
last = first;
}
else
{
// Add to end of existing list
last.next = new Node(itnum,Catg,Desc,val);
last = last.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.id + "\t");
   strBuilder.append(p.Category + "\t");
   strBuilder.append(p.Description + "\t");
   strBuilder.append(p.value + "\n");
   p = p.next;
}
return strBuilder.toString();
}



// Main method to test the linkedlist
public static void main(String [] args)
{
LinkedList ll = new LinkedList();
ll.add(1,"food","Apple",2);
ll.add(2,"Coins","GoldCoins",2);
System.out.println("The members of the list are:");
System.out.print(ll);
}
}

Answer 1

/**
The LinkedList class implements a Linked list that contains inventory
*/

class LinkedList
{
/**
The Node class stores a list element
and a reference to the next node.
*/

private class Node
{
int id; //Item Number
String Category; //category
String Description; // Description
int value;//value
Node next;

/**
Constructor.
@param val The element to store in the node.
@param n The reference to the successor node.
*/

Node(int itnum, String Catg, String Desc, int val, Node n)
{
id = itnum;
Category = Catg;
Description = Desc;
value = val;
next = n;
}

/**
Constructor.
@param val The element to store in the node.
*/

Node(int itnum, String Catg, String Desc, int val)
{
// Call the other (sister) constructor.
id = itnum;
Category = Catg;
Description = Desc;
value = val;
}
}

private Node first; // list head
private Node last; // last element in list

/**
Constructor.
*/

public LinkedList()
{
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 or start of list
depends on addTostart value
@param e The value to add to the
end of the list.
*/

public void add(int itnum, String Catg, String Desc, int val, boolean addTostart )
{
if (isEmpty())
{
first = new Node(itnum,Catg,Desc,val);
last = first;
}
else
{
if(!addTostart){
// Add to end of existing list
last.next = new Node(itnum,Catg,Desc,val);
last = last.next;
}else{
// Add to start of existing list
   Node temp = new Node(itnum,Catg,Desc,val);
   temp.next = first;
   first = temp;
}
}
}
/**
The remove method removes an element from
the end of the list.
  
*/
public void remove(){
if (isEmpty())
{
   return;
}else{
   Node p = first;
   Node n = first.next; // to point to last but one node
   if(n != null){
       Node nn = n.next; //to point to last node
   while ( nn != null)
   {
           //System.out.print(nn.id);
       p = n;
       n = nn;
       nn = nn.next;
      
   }
   //nn is null ie n is last but one node
   //System.out.print(p.id);
   p.next = null;
}else{
       first = null;
}
}
}

/**
The delete method removes an element from
the list based on itnum.
  
*/
public void delete(int itnum){
if (isEmpty())
{
   return;
}else{
   Node p = first;
   Node n = first.next; // to point to last but one node
   boolean matchFound = false;
   if(first.id == itnum){
       first = first.next;
   }
   if(n != null){
       Node nn = n.next; //to point to last node
   while ( nn != null )
   {
       if(nn.id == itnum){
           matchFound = true;
           break;
       }
       p = n;
       n = nn;
       nn = nn.next;
      
   }
   if(matchFound)
   //nn is the node to be deleted ie n is last but one node
   p.next = n.next;
}else{
       if(first.id == itnum){
       first = null;
       }
}
}
}

/**
Print inventory by category
  
*/
public void printInventory(String Catg){
   Node p = first;
   StringBuilder strBuilder = new StringBuilder();
while (p != null )
{
       if(p.Category.equals(Catg)){
       strBuilder.append(p.id + "\t");
   strBuilder.append(p.Category + "\t");
   strBuilder.append(p.Description + "\t");
   strBuilder.append(p.value + "\n");
   }
   p = p.next;
     
}
System.out.print("printing inventory by category "+Catg+"\n"+strBuilder.toString());
}

/**
How many items in each category
*/

public int sizeByCategory(String catg)
{
int count = 0;
Node p = first;
while (p != null )
{
// There is an element at p
if(p.Category.equals(catg))
count ++;
p = p.next;
}
return count;
}

/**
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.id + "\t");
strBuilder.append(p.Category + "\t");
strBuilder.append(p.Description + "\t");
strBuilder.append(p.value + "\n");
p = p.next;
}
return strBuilder.toString();
}

// Main method to test the linkedlist
public static void main(String [] args)
{
LinkedList ll = new LinkedList();
ll.add(1,"food","Apple",2,false);
ll.add(2,"Coins","GoldCoins",2,false);
ll.add(3,"Coins","SilverCoins",2,false);
ll.add(4,"food","Banana",2,false);
System.out.println("The members of the list are:");
System.out.print(ll);

int coinsCount = ll.sizeByCategory("Coins");
System.out.println("number of items in Coins category:"+coinsCount);
ll.printInventory("Coins");
ll.remove();
System.out.println("After remove The members of the list are:");
System.out.print(ll);
ll.delete(1);

System.out.println("After delete The members of the list are:");
System.out.print(ll);
}
}