delete () in linkedlist in Java without using API

[Surya Bavirti]

Given the following classes, wite the delete() method, which will delete all nodes equal() to Node n. delete() should return true if at least one node could be removed, and return false otherwise. Use Java syntax.Don't use Java API.
Here is my code for delete().But i'm unable to get the correct result.What my problem is, if the Node 'n' is existing multiple times,my delete() will not remove all 'n's.It removes only one 'n'.Pla help me.

My code for delete()
--------------------

public boolean delete(Node n) { /* Provide code for this method */ }
{
    LinkedList myList = new LinkedList();
    int var = 0;
 
    Node head = new DS().getStart(); 
    if (head.equal(n) )
    {
        head =  head.getNext();
        setStart(head);     
        var++;
    }
 
    Node n1 = null;
 
    for (Node l = new DS().getStart() ; l != null; l = l.getNext())
    {
        if (l.equal(n))
        {
            n1.setNext(l.getNext());
            var++;
        }
    }
    if (var > 0)
        return true;
    else 
        return false;
}

----------------------------// end of delete()


Actual Program
---------------

Public class DS {
 
    public Node getStart() { 
        /* This method is written for you – it will return the first node */ 
    }
 
    public void setStart(Node n) {
        /* This method is written for you – it will set the first node */ 
    }
 
    public boolean delete(Node n) { /* Provide code for this method */ }

    class Node {

        public boolean equal(Node n) { /* This method is written for you */ }
 
        public Node getNext() { 
            /* This method is written for you – it will return the next node*/ 
        }
 
        public Node getPrevious() { 
            /* This method is written for you – it will return the previous node*/ 
        }
 
        public void setNext(Node n) { 
            /* This method is written for you – it will set the next node*/ 
        }
 
        public void setPrevious(Node n) { 
            /* This method is written for you – it will set the previous node*/ 
        }
    }
}

[RP]Added code tags, modified indentation[/RP]
[ September 25, 2008: Message edited by: Rob Prime ]

[Garrett Rowe]

Forget the Java code for a moment. Try to explain the delete algorithm you want to implement in English.

[Surya Bavirti]

The delete() method, which will delete all nodes equal() to Node n. delete() should return true if at least one node could be removed, and return false otherwise. Use Java syntax.Don�t use java API

[Garrett Rowe]

I understand what you're supposed to do. How do you propose to do it?

[Rob Spoor]

Some comments:

LinkedList myList = new LinkedList();

LinkedList? As in java.util.LinkedList? You're not supposed to be using that. In fact, you're not. You create it, then ignore it. Just remove this line.

Node head = new DS().getStart();

You create a new DS instance, then call getStart on that. You probably want to call getStart on the current instance; either use "this.getStart()" or simply "getStart()".

if (head.equal(n) )

You could turn that in a while loop. What if the first three nodes are equal to the node to remove?

for (Node l = new DS().getStart() ; l != null; l = l.getNext())

Again, new DS().

n1.setNext(l.getNext());

That will 100% surely throw a NullPointerException. You've set n1 to be null, then never reassign it. You need to set it to something somewhere, and also check if it is null - it probably will during the first iteration.

if (var > 0)
    return true;
else 
    return false;

You can also just return (var > 0) - that's a boolean all by itself


You basically have the right idea, it just needs some tweaking.


And one final note: getStart() is surely to return null if the list is empty. What do you do then?


Oh, and in the future, please Use Code Tags. I've added them for you this time.
[ September 25, 2008: Message edited by: Rob Prime ]

[Surya Bavirti]

Thanks RobPrime.Good Suggestions