Question

How do I implement a queue from a single linked list?

Asked by: datopdogg7

Hi experts, the below code is of a single linked list.
I need to implement a queue (FIFO) from this very code.
Can you please tell me what I need to add and change in this code to make it a stack class?
Please no references to other websites, I have already looked, and I would like to make use of my existing code.
Thanks,
Dennis

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
 
package assignment1;
 
 
public class LinkedList {
    
    // Make variables private
 
    private Node head;
    private int listCount;
 
        // Constructor for the class
    
        public LinkedList()
        {
                // this is an empty list, so the reference to the head node
                // is set to a new node with no data
                head = new Node(null);
                listCount = 0;
        }
 
        // This method appends the word to the end of this list or in between two words in doing so making the list alphabetic
        
        public void add(Word data)
 
        {
                Node temp = new Node(data);
                Node current = head;
                
                // Crawl to the end of the list, starting from the head node
 
                while(current.getNext() != null && current.getNext().getData().getWord().compareTo(data.getWord())<0)
                {
                        current = current.getNext();
                }
                
                // Make the new node's reference equal to the last node's "next" reference 
 
                temp.setNext(current.getNext());
                current.setNext(temp);
                
                // Increment the number of word objects in the list
                
                listCount++;
        }
 
        // Inserts the word at the specified position in this list.        
        
        public void add(Word data, int index)
 
        {
                Node temp = new Node(data);
                Node current = head;
                // crawl to the requested index or the last element in the list,
                // whichever comes first
                for(int i = 1; i < index && current.getNext() != null; i++)
                {
                        current = current.getNext();
                }
                // set the new node's next-node reference to this node's next-node reference
                temp.setNext(current.getNext());
                // now set this node's next-node reference to the new node
                current.setNext(temp);
                listCount++;// increment the number of elements variable
        }
 
        public Word get(int index)
        // post: returns the element at the specified position in this list.
        {
                // index must be 1 or higher
                if(index <= 0)
                        return null;
 
                Node current = head.getNext();
                for(int i = 1; i < index; i++)
                {
                        if(current.getNext() == null)
                                return null;
 
                        current = current.getNext();
                }
                return current.getData();
        }
 
        public boolean remove(int index)
        // post: removes the element at the specified position in this list.
        {
                // if the index is out of range, exit
                if(index < 1 || index > size())
                        return false;
 
                Node current = head;
                for(int i = 1; i < index; i++)
                {
                        if(current.getNext() == null)
                                return false;
 
                        current = current.getNext();
                }
                current.setNext(current.getNext().getNext());
                listCount--; // decrement the number of elements variable
                return true;
        }
 
        public int size()
        // post: returns the number of elements in this list.
        {
                return listCount;
        }
 
        public Word returnWord(String user_word){
 
            Word word = new Word();
            Node current = head.getNext();
 
            for(int i = 1; i < listCount; i++)
            {
                    current = current.getNext();
 
                    if(current.getData().getWord().compareTo(user_word) == 0){
 
                    break;
 
                    }
 
            }
 
            return current.getData();
 
        }
 
        public boolean checkWord(String user_word){
 
            Word word = new Word();
            Node current = head.getNext();
            boolean answer = false;
            int i = 1;
 
            if(listCount != 0){
 
                current = current.getNext();
 
                do
                {
                        current = current.getNext();
 
                        if(current.getData().getWord().compareTo(user_word) == 0){
 
                            answer = true;
 
                        }
 
                        else{
 
                            answer = false;
 
                        }
 
                }while(i < listCount);
            }
 
            return answer;
 
        }
 
        private class Node
        {
                // reference to the next node in the chain,
                // or null if there isn't one.
                Node next;
                // data carried by this node.
                // could be of any type you need.
                Word data;
 
 
                // Node constructor
                public Node(Word _data)
                {
                        next = null;
                        data = _data;
                }
 
                // another Node constructor if we want to
                // specify the node to point to.
                public Node(Word _data, Node _next)
                {
                        next = _next;
                        data = _data;
                }
 
                // these methods should be self-explanatory
                public Word getData()
                {
                        return data;
                }
 
                public void setData(Word _data)
                {
                        data = _data;
                }
 
                public Node getNext()
                {
                        return next;
                }
 
                public void setNext(Node _next)
                {
                        next = _next;
                }
        }
 
 
}

                                  
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Asked On
2009-02-04 at 18:36:04ID24114344
Tags

JAVA

Topic

Java Programming Language

Participating Experts
3
Points
500
Comments
10

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Answers

 

by: objectsPosted on 2009-02-04 at 18:45:08ID: 23556017

public class Queue
{
   private LinkedList list = new LinkedList();

   // now add your public class Stack
{
   private LinkedList list = new LinkedList();

   // now add your Stack methods and pave them operate on list

   public void push(Object o)
   {
       list.add(o);
   }

   public Object pop()
   {
       Object result = list.get(0);
       list.remove(0);
       return result;
   }

 

by: Ajay-SinghPosted on 2009-02-04 at 20:29:26ID: 23556474

You also need to override add method of the LinkedList and add to the
head to the list (as oppose to adding to the tail of the list).

 

by: Ajay-SinghPosted on 2009-02-04 at 20:30:14ID: 23556478

I am sorry about my comment, I was confused with the Stack question

 

by: datopdogg7Posted on 2009-02-04 at 22:30:43ID: 23556998

Sorry there was a typo in my description.
It should have read:

Hi experts, the below code is of a single linked list.
I need to implement a queue (FIFO) from this very code.
Can you please tell me what I need to add and change in this code to make it a queue class?
Please no references to other websites, I have already looked, and I would like to make use of my existing code.
Thanks,
Dennis

 

Please update your answers so I can reward points. Thanks!

 

by: objectsPosted on 2009-02-04 at 22:33:50ID: 23557005

what i posted above is a queue, let me know if ypou need help with any other methods than what I posted above.

 

by: datopdogg7Posted on 2009-02-04 at 22:41:27ID: 23557030

Isn't the above the same as the stack code you gave in my other question though? The code still uses the push and pop

 

by: objectsPosted on 2009-02-04 at 22:44:22ID: 23557040

difference is queue.push adds to end of list, and stack.push adds to start of list

 

by: datopdogg7Posted on 2009-02-04 at 22:50:27ID: 23557056

ah of course. i should have read it more carefully, thanks!

 

by: LTIndiaPosted on 2009-02-04 at 23:14:15ID: 23557133

public class Queue
{
   private LinkedList list = new LinkedList();

   // now add your Queue methods as wrappers on list
    public int size()
   // post: returns the number of elements in this Queue.
   {
         return list.size();
   }

   public void EnqueueData(Word data)
   {
       list.add(data);
   }

   public Word DequeueData()
   {
       Word result = list.get(1);      // As You have implemented 1 as starting index
       list.remove(1);
       return result;
   }
}

 

by: datopdogg7Posted on 2009-02-04 at 23:30:18ID: 23557193

Thanks LTindia,

Would I implement your code in addition with Objects code?

20120131-EE-VQP-002

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