Question

Java Programming:

The following is my code:

public class KWSingleLinkedList<E> {
   public void setSize(int size)
   {
       this.size = size;
   }

   /** Reference to list head. */
   private Node<E> head = null;
   /** The number of items in the list */
   private int size = 0;
  
   /** Add an item to the front of the list.
   @param item The item to be added
   */
   public void addFirst(E item) {
       setHead(new Node<>(item, getHead()));
       size++;
   }
      
   /** Add a node after a given node
   @param node The node preceding the new item
   @param item The item to insert
   */
   private void addAfter(Node<E> node, E item) {
       node.next = new Node<>(item, node.next);
       size++;
   }  
  
   /** Remove the node after a given node
   @param node The node before the one to be removed
   @return The data from the removed node, or null
   if there is no node to remove
   */
   @SuppressWarnings("unused")
   private E removeAfter(Node<E> node) {
       Node<E> temp = node.next;
      
       if (temp != null) {
           node.next = temp.next;
           size--;
           return temp.data;
       }
       else {
           return null;
       }
   }  
  
   /** Remove the first node from the list
   @return The removed node's data or null if the list is empty
   */
   @SuppressWarnings("unused")
   private E removeFirst() {
       Node<E> temp = getHead();
       if (getHead() != null) {
           setHead(getHead().next);
       }
       // Return data at old head or null if list is empty
       if (temp != null) {
           size--;
           return temp.data;
       }
       else {
           return null;
       }
   }
  
   /** Find the node at a specified position
   @param index The position of the node sought
   @return The node at index or null if it does not exist
   */
   private Node<E> getNode(int index) {
       Node<E> node = getHead();
       for (int i = 0; i < index && node != null; i++) {
           node = node.next;
       }
       return node;
   }
  
   /** Get the data at index
   @param index The position of the data to return
   @return The data at index
   @throws IndexOutOfBoundsException if index is out of range
   */
   public E get(int index) {
       if (index < 0 || index >= size) {
           throw new IndexOutOfBoundsException(Integer.toString(index));
       }
       Node<E> node = getNode(index);
       return node.data;
   }
  
   /** Store a reference to anEntry in the element at position index.
   @param index The position of the item to change
   @param newValue The new data
   @return The data previously at index
   @throws IndexOutOfBoundsException if index is out of range
   */
   public E set(int index, E newValue) {
       if (index < 0 || index >= size) {
           throw new IndexOutOfBoundsException(Integer.toString(index));
       }
      
       Node<E> node = getNode(index);
       E result = node.data;
       node.data = newValue;
      
       return result;
   }  
  
   /** Insert the specified item at index
   @param index The position where item is to be inserted
   @param item The item to be inserted
   @throws IndexOutOfBoundsException if index is out of range
   */
   public void add(int index, E item) {
       if (index < 0 || index > size) {
           throw new IndexOutOfBoundsException(Integer.toString(index));
       }
      
       if (index == 0) {
           addFirst(item);
       }
       else {
           Node<E> node = getNode(index-1);
           addAfter(node, item);
       }
   }  
  
   /** Append item to the end of the list
   @param item The item to be appended
   @return true (as specified by the Collection interface)
   */
   public boolean add(E item) {
       add(size, item);
       return true;
   }      
  
   public Node<E> getHead() {
       return head;
   }

   public void setHead(Node<E> head) {
       this.head = head;
   }
  
   public String toString() {
   @SuppressWarnings("unchecked")
       Node<String> nodeRef = (Node<String>) head;
       StringBuilder result = new StringBuilder();
       while (nodeRef != null) {
       result.append(nodeRef.data);
       if (nodeRef.next != null) {
       result.append(" ==> ");
       }
      
       nodeRef = nodeRef.next;
       }
       return result.toString();
   }

   public int remove(E item) {
       if(head == null) {
       return -1;
       }
       if(head.data.equals(item)) {
           head = head.next;
           size--;
           return 0;
       }
      
       int index = 1;
       Node<E> node = head;
      
       while(node.next != null) {
           if(node.next.data.equals(item)) {
               node.next = node.next.next;
               size--;
               return index;
           }
       }
       return -1;
   }
  
   /** Return the size of the linked list.
   */
   public int getSize() {
       return size;
   }     

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I need help implementing the following method:

/** Insert a new item before the one at position index,
   starting at 0 for the list head. The new item is inserted between the one
   at position index-1 and the one formerly at position index.
   If the index is zero, add the new item to the first
   @param index The index where the new item is to be inserted
   @param item The item to be inserted
   @throws IndexOutOfBoundsException if the index is out of range
   */
  
   // You should take a look at addAfter(Node<E> node, E item)
   // You need to consider two situations: index == 0 and index > 0
   // Hint:
   // 1. Check whether the index is valid
   // 2. if index == 0, create a new node with item and refer to this.head
   // and set the new node to this.head, using the constructor: Node(E dataItem, Node<E> nodeRef):
   // this.head = new Node<>(item, this.head);
   // 3. Otherwise, Node<E>node = getNode(index-1), and use item and node.next to create a new node
   // and give the new node to node.next.
   // 4. Don't forget to update the size
   public void addBefore(int index, E item) {
       // Add your code here
      
   }

Answer 1

Code

Code

You didn't provid the Node class so i have created my own class

/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
/**
*
* @author JOSEE
*/
public class Node <E> {
E data;
Node next;

public Node(E data, Node next) {
this.data = data;
this.next = next;
}
      
}

KWSingleLinkedList.java

public class KWSingleLinkedList<E> {
public void setSize(int size)
{
this.size = size;
}

/** Reference to list head. */
private Node<E> head = null;
/** The number of items in the list */
private int size = 0;
  
/** Add an item to the front of the list.
@param item The item to be added
*/
public void addFirst(E item) {
setHead(new Node<>(item, getHead()));
size++;
}
  
/** Add a node after a given node
@param node The node preceding the new item
@param item The item to insert
*/
private void addAfter(Node<E> node, E item) {
node.next = new Node<>(item, node.next);
size++;
}
  
/** Remove the node after a given node
@param node The node before the one to be removed
@return The data from the removed node, or null
if there is no node to remove
*/
@SuppressWarnings("unused")
private E removeAfter(Node<E> node) {
Node<E> temp = node.next;
  
if (temp != null) {
node.next = temp.next;
size--;
return temp.data;
}
else {
return null;
}
}
  
/** Remove the first node from the list
@return The removed node's data or null if the list is empty
*/
@SuppressWarnings("unused")
private E removeFirst() {
Node<E> temp = getHead();
if (getHead() != null) {
setHead(getHead().next);
}
// Return data at old head or null if list is empty
if (temp != null) {
size--;
return temp.data;
}
else {
return null;
}
}
  
/** Find the node at a specified position
@param index The position of the node sought
@return The node at index or null if it does not exist
*/
private Node<E> getNode(int index) {
Node<E> node = getHead();
for (int i = 0; i < index && node != null; i++) {
node = node.next;
}
return node;
}
  
/** Get the data at index
@param index The position of the data to return
@return The data at index
@throws IndexOutOfBoundsException if index is out of range
*/
public E get(int index) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException(Integer.toString(index));
}
Node<E> node = getNode(index);
return node.data;
}
  
/** Store a reference to anEntry in the element at position index.
@param index The position of the item to change
@param newValue The new data
@return The data previously at index
@throws IndexOutOfBoundsException if index is out of range
*/
public E set(int index, E newValue) {
if (index < 0 || index >= size) {
throw new IndexOutOfBoundsException(Integer.toString(index));
}
  
Node<E> node = getNode(index);
E result = node.data;
node.data = newValue;
  
return result;
}
  
/** Insert the specified item at index
@param index The position where item is to be inserted
@param item The item to be inserted
@throws IndexOutOfBoundsException if index is out of range
*/
public void add(int index, E item) {
if (index < 0 || index > size) {
throw new IndexOutOfBoundsException(Integer.toString(index));
}
  
if (index == 0) {
addFirst(item);
}
else {
Node<E> node = getNode(index-1);
addAfter(node, item);
}
}
  
/** Append item to the end of the list
@param item The item to be appended
@return true (as specified by the Collection interface)
*/
public boolean add(E item) {
add(size, item);
return true;
}
  
public Node<E> getHead() {
return head;
}

public void setHead(Node<E> head) {
this.head = head;
}
  
public String toString() {
@SuppressWarnings("unchecked")
Node<String> nodeRef = (Node<String>) head;
StringBuilder result = new StringBuilder();
while (nodeRef != null) {
result.append(nodeRef.data);
if (nodeRef.next != null) {
result.append(" ==> ");
}
  
nodeRef = nodeRef.next;
}
return result.toString();
}

public int remove(E item) {
if(head == null) {
return -1;
}
if(head.data.equals(item)) {
head = head.next;
size--;
return 0;
}
  
int index = 1;
Node<E> node = head;
  
while(node.next != null) {
if(node.next.data.equals(item)) {
node.next = node.next.next;
size--;
return index;
}
}
return -1;
}
  
/** Return the size of the linked list.
*/
public int getSize() {
return size;
}   

//I need help implementing the following method:

/** Insert a new item before the one at position index,
starting at 0 for the list head. The new item is inserted between the one
at position index-1 and the one formerly at position index.
If the index is zero, add the new item to the first
@param index The index where the new item is to be inserted
@param item The item to be inserted
@throws IndexOutOfBoundsException if the index is out of range
*/
  
// You should take a look at addAfter(Node<E> node, E item)
// You need to consider two situations: index == 0 and index > 0
// Hint:
// 1. Check whether the index is valid
// 2. if index == 0, create a new node with item and refer to this.head
// and set the new node to this.head, using the constructor: Node(E dataItem, Node<E> nodeRef):
// this.head = new Node<>(item, this.head);
// 3. Otherwise, Node<E>node = getNode(index-1), and use item and node.next to create a new node
// and give the new node to node.next.
// 4. Don't forget to update the size
public void addBefore(int index, E item) {

if (index < 0 || index > size) {
throw new IndexOutOfBoundsException(Integer.toString(index));
}
  
if (index == 0) {
Node newNode=new Node(item,head);
this.head=newNode;
return;
}
Node nextNode=this.head;
Node prev=nextNode;
int i=0;
while(nextNode!=null)
{
if(i==index)
break;
prev=nextNode;
nextNode=nextNode.next;
i++;
}
Node newNode=new Node(item,null);
prev.next=newNode;
newNode.next=nextNode;   
}
}

test.java

public class test {

/**
* @param args the command line arguments
*/
public static void main(String[] args) {
KWSingleLinkedList<String> list=new KWSingleLinkedList<>();

list.add("One");
list.add("Three");
list.addBefore(1, "Two");

System.out.println(list);
}
  
}

output

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