gistfile1.java

/**
 * MyList
 * 
 * ASSIGNMENT   Assignment 2, Question 1
 * @author      Brittany Postninkoff, 07757816
 * @version     2014 - 06 - 07 
 * 
 * PURPOSE:     This is a class that builds a linked list.
 */

import java.util.*;

public class MyList
{
    private Link first;
    private Link temp;

    /**
     * This is a constructor for MyList.
     */
    public MyList()
    {
        first = null;
        temp = null;
    }

    /**
     * Adds the new link to the front of the linked list.
     * 
     * @param       Object data         The value to be used in creating a new
     *                                    link for the linked list.
     */
    public void addFirst(Object data)
    {
        Link newFirst = new Link(data);        
        //Sets the current first link, to the new link's next link, and sets 
        //  the new link to the first position
        newFirst.setNext(first);
        first = newFirst;
    }

    /**
     * Adds a link to the end of the linked list.
     * 
     * @param       Object data         The value to be used in creating a new 
     *                                    link to add onto the end of the list.
     */
    public void addLast(Object data)
    {
        Link newLink = new Link(data);

        //Checks to see if the first link is null. If so, the first link is
        //  the new link and requires no shifting. 
        if(first == null)
        {
            first = newLink;
            first.setNext(null);
        }
        else
        {
            temp = first;

            //iterates through the linked list until reaching the point just
            //  before the end of the list
            while(temp.getNext() != null)
            {
                temp = temp.getNext();
            }

            //Instead of being null, the last link is now the value of the
            //  new link that was just created. 
            temp.setNext(newLink);
        }
    }

    /**
     * Removes the first item in the linked list.
     */
    public void removeFirst()
    {
        //If there is an item in the list.
        if(first != null)
        {
            //If there is only one item in the list.
            if (first.getNext() == null)
            {
                first = null;   
            }
            else
            {
                //First is now adjusted to be the second item in the list.
                first = first.getNext();
            }
        }
    }    

    /**
     * Removes the last item in the list.
     */
    public void removeLast()
    {
        //If first and last are the same item, reset linked list.
        if (first.getNext() == null)
        {
            first = null;
        }
        else
        {
            //Set to the first link so we can loop through.
            temp = first;

            //Loop through to the next to last link.
            while(temp.getNext() != null)
            {
                temp = temp.getNext();
            }

            temp.setNext(null);
        }

    }    

    /**
     * Returns the data inside a link. Loops through the list, until a certain
     *   position in the list, and returns the link data.
     *   
     * @param       int index       The position of the link to be printed.
     * 
     * @return      Object data     The data inside the link in question.
     */
    public Object get(int index)
    {
        temp = first;
        Object data = "";

        //Loops through until the correct link
        for(int i = 0; i < index; i++)
        {
            temp = temp.getNext();
        }

        return temp.getData();
    }

    /**
     * Checks to verify whether the list is empty or not.
     * 
     * @return      boolean empty       If list is empty, this value is true.
     */
    public boolean isEmpty()
    {
        boolean empty = true;

        if(first.getNext() != null)
        { 
            empty = false;
        }

        return empty;
    }

    public String toString()
    {
        String values = "";
        
        Link current = first;
        
        while(current != null)
        {
            values = current.getData() + "\n";
            current = current.getNext();
        }
        
        return values;
    }
}