Linked List FIFO queu correction in Java

Question

i am new to Java bro-gramming(about 4 months). I have just picked up a copy of "Data Structures & Algorithms in Java" Second Edition by Robert Lafore and i am reading chapters and attempting the problems at the back. Since i am not taking an official class, i need some form of grading to teach me how my work can be improved.. what better place than the geniuses on the stack.

I am currently on chapter 5, Linked-Lists.

Here is problem 5.1 Implement a priority queue based on a sorted linked list. The remove operation on the priority queue should remove the item with the smallest key.

Container class

public class LinkLL {


public static LinkLL leftConnector; //left side of node
public static String fName; //item in actual node
public static LinkLL rightConnector; //Right side of node


public LinkLL(String key)
{
    fName = key; 
    //A new LinkLL linked list has been Instantiated, 
    //although it is empty.

    rightConnector = null;
    leftConnector = null;
}


public void showName()
{
    System.out.print(fName + " " + "There are " + SortedLL.nElems + "in the list at this moment.");

}

}

here we have methods such as insert, delete..etc. I feel like i did a good job on the "insert" and maybe the delete? but my "sort" and "display" are giving me a run for my money. For instance, i want to display EVERY string inputted, but the way i have it, only the first one shows.

"Abstraction"

public class SortedLL {

static LinkLL currentNode;
static LinkLL firstNode;
static final LinkLL lastNode = null;
static LinkLL prequelNode;
static LinkLL sequelNode;
static float nElems;
static LinkLL l;

public static void insert(String key)
{
    if ( nElems == 0) //could have also been if(nElems == 0)
    {   
        l = new LinkLL(key); //if nothing exists, create one
        l.rightConnector = sequelNode;//the right connector is equal to the sequelNode
        sequelNode = lastNode;  // Sequel Node is equal to lastNode which is 'null'.
        prequelNode = sequelNode;
        firstNode.leftConnector = lastNode;
    }

    else if( !(nElems == 0) )
    {
        LinkLL NewEndNode;
        NewEndNode = lastNode;
        l.rightConnector = NewEndNode;
        l.leftConnector = prequelNode.rightConnector;           

    }
    //when such occurs, nodes must be re-connected
    nElems++;
}

public void remove()
{   

    if(nElems == 0) System.out.println("There are no items to remove.");
    //if( !find(key) ) System.out.println(key +" could not be located, " + "and thus cannot be removed.");


        //while ( find(key)  ) //while the key can be found
        {
            //currentNode = key;

            prequelNode.rightConnector = sequelNode.leftConnector;


            nElems--;
        }
    //when such occurs, nodes should be reconnected

}

public boolean find(LinkLL key)
{
    if (isEmpty() == true)
    {
        System.out.println("The List is Empty");
    }

    else
    {
        for(int i = 0; i<nElems+1; i++) 
        {
            if (i == nElems+1) 
            //added '+1' to make sure that the item to be searched for is not at the bottom(list scanned throughly)
                System.out.println("The key " + key + "has NOT been found!");
            else 
                System.out.println("The key " + key + "has been found!");
        }

    }
    return true;
}


public void sort()
{


}

public boolean isEmpty()
{
    if (firstNode != null) return false;
    else return false;
}

public void displayNode()
{
    LinkLL first = null;
    LinkLL current = first ;

    while (current != null)
    {
        l.showName();
        current = current.rightConnector;

    }       
}

}

Main()

public class sortedLLApp {
public static void main(String []args)
{
    SortedLL s = new SortedLL();

    s.isEmpty();

    s.insert("Jack");
    s.insert("Jill");
    s.insert("John");
    s.insert("Jenn");
    s.insert("James");
    s.displayNode();



}

}

Answer 1

Well obviously sort does nothing because you haven't implemented it at all. But maybe you should try it some and submit it as a separate question.

---

The reason your displayNode() does nothing is that the whole method uses local variables. Also, for some reason you've declared most of your code as static, which entirely defeats the purpose of having a reusable class. Admittedly, I haven't actually run your code yet, but why don't you try this:

1. Remove all instances of the word static from the SortedLL class.
2. Change displayNode() to this:

Code:

public void displayNode()
{
    LinkLL current = firstNode;

    while (current != null)
    {
        l.showName();
        current = current.rightConnector;
    }       
}