java - bubble sort implementation on linked lists

Question

I have to implement a BubbleSort algorithm on a Linked List instead of an array. I'm new to java so I don't really know how to put it in code. But I gave it a try and here's what I got:

SinglyNode.java

public class SinglyNode
{
public Object names;
public SinglyNode next;

public SinglyNode (Object name1)
{
    names = name1;
}

public SinglyNode (Object name2, SinglyNode next1)
{
    names = name2;
    next = next1;
}

Object getObject()
{
    return names;
}

SinglyNode getNext()
{
    return next;
}

void displayLink()
{
    System.out.print("{" + names + "}");
}
}

LinkList.java I think my problem is here in the method. I dunno how to implement the BubbleSort so it would sort the Object names in ascending order.

public class LinkList
{
SinglyNode first;

public boolean isEmpty()
{
    return (first == null);
}

void insertFirst(Object name1)
{
    SinglyNode newNode1 = new SinglyNode(name1);
    newNode1.next = first;
    first = newNode1;
}

SinglyNode delete(Object name2)
{
    SinglyNode temp = first;
    first = first.next;
    return temp;
}

void display()
{
    System.out.print("LIST: 
");
    SinglyNode current = first;
    while(current != null)
    {
        current.displayLink(); // print data
        current = current.next; // move to next link
    }
    System.out.println("
");
}
//////////////////////////////////////////////////////    
void bubbleSort()
{ 
    Object n = first;
    Object temp = first;

    if (na.compareTo(first) < first.compareTo(na))
    {
        temp = na.compareTo(first);
    } else {
        temp = first.compareTo(na);
    }
    System.out.println(temp);

}

private void swap(Object one, Object two)
{ 
    Object temp = one.names;
    one.names = two.names;
    two.names = temp; 
}
}

SinglyLinkList.java

public class SinglyLinkList
{
public static void main (String args[])
{
    LinkList list = new LinkList();

    list.insertFirst("Squirtle");
    list.insertFirst("Bulbasaur");
    list.insertFirst("Charmander");
    list.insertFirst("Pichu");
    list.insertFirst("Ghastly");
    list.insertFirst("Mewtwo");
    list.insertFirst("Dialga");

    list.display();
    list.bubbleSort();
    list.display();

}
}

Answer 1

In your list it will help to have a size field, to store the number of elements in the list. Also make the class SinglyNode implement Comparable so the compareTo method behaves as you want. The in-place swapping of two elements in Single LinkedList is actually quite involved, and the performance is really bad!

public void bubbleSort
{
  for (int i = 0; i < size; i++)
  {
    for (int j = i; j < size; j++)
    {
       if (elementAt(j).compareTo(elementAt(j+1)) > 0)
       {
          swap(j, j + 1);
       }
    }
  }
}

public SinglyNode elementAt(int index)
{
   SinglyNode temp = first;

   for (int i = 0, i < index; i++)
   {
      temp = temp.getNext();
   }

   return temp;
}

public void swap(int firstIndex, int secondIndex)
{
   SinglyNode secondNext = elementAt(secondIndex).getNext();       
   SinglyNode second = elementAt(secondIndex);
   SinglyNode first = elementAt(first);
   SinglyNode firstPrevious = elementAt(first - 1);


   firstPrevious.setNext(second);
   first.setNext(secondNext);
   second.setNext(first);
}