node class for linked list

[Ronald Pruitt]

I have the following code and want to check the methods. I know I have to create the nodes but I don't know what to put in the brackets to do this. can anyone help?
I'm really getting brain cramp.

class Link
{
private Object element;// Object for this node
private Link next;// pointer to next node in list
/*************************************************************************************
Constructor 1
*************************************************************************************/
Link(Object it, Link nextval)
{
element = it;// Given Object
next = nextval;
}
/*************************************************************************************
Constructor 2
*************************************************************************************/
Link(Link nextval)
{
next = nextval;
}
Link next()
{
return next;
}
Link setNext(Link nextval)
{
return next = nextval;
}
Object element()
{
return element;
}

Object setElement(Object it)
{
return element = it;
}
public static void main(String[] args)
{
Object knit = new Object();
Object one = new Object();
Object pearl = new Object();
Object two = new Object();
}

}         

I've tried putting Object and nextval and element, etc. but that evidently isn't correct becaus I keep getting errors with everything I've tried. How do I test Please!!!
Thanks in advance for any advice.
[This message has been edited by Ronald Pruitt (edited January 28, 2001).]

[Val Dra]

Here is how i designed by own node class
[<code>]
private class Node {
private Node next;
private Node previouse;
private Object data;
private void setNext( Object o ) {
next = ( Node )o;
}
private void setPreviouse( Object o ) {
previouse = ( Node )o;
}
private void setData( Object o ) {
data = o;
}
private Node getNext() { return next;}
private Node getPreviouse() { return previouse;}
private Object getData() { return data;}
}
[</code>]

[Ronald Pruitt]

I thank you but that doesn't explain how to test the methods, how do I test the methods without creating a couple of nodes, and how do I do that?

[Val Dra]

The thing is this is just a part of it. The Node class will just hold a one object . But what you now need is , is to design a list object which will bind nodes together.

[Nathan Pruett]

Ronald,
Val is right... you have to make a linked list out of your nodes to test them. Here's something you could do with the Link class you posted :

public class MyLinkedList //Since Java already has a LinkedList class
{
    private final Link head;  //holds start of list
    private Link current;  //holds current link we are looking at
    MyLinkedList()  //constructor
    {
        head = current = new Link( (Object)null, (Link)null );
    }
    public void next ( )  //Moves through the list
    {
        if ( current.next() != null )
        {
            current = current.next();
        }
    }
    public Object currentValue ( )  //Returns current value w/o deleting Link
    {
        return current.element();
    }
    public void put ( Object o )  //puts object in list
    {
        Link temp = head;
        while ( temp.next() != null )  //This gets us to the end
        {
            temp = temp.next();
        }
        temp.setNext( new Link (o, (Link)null) );
        if ( current == head )
        {
            current = head.next();
        }
    }
    public Object get()  //gets the current object from the list
    {
        Link temp = head;
        Object toBeReturned;
        while ( temp.next() != current )  //finds Link before current
        {
            temp = temp.next();
        }
        toBeReturned = current.element();
        temp.setNext( current.next() );
        current = temp;
        return toBeReturned;
    }
    public String toString()
    {
        Link temp = head;
        String toBeReturned = "";
        while ( temp != null )
        {
            if ( temp.element() != null )
            {
                toBeReturned += ( (temp.element()).toString() ) + " ";
            }
            temp = temp.next();
        }
        return toBeReturned;
    }
    public static void main( String args[] )
    {
        String knit = "knit";
        String one  = "one";
        String perl = "perl";
        String two  = "two";
        MyLinkedList mll = new MyLinkedList();
        mll.put( knit );
        mll.put( one );
        mll.put( perl );
        mll.put( two );
        System.out.println( mll );
        while ( !(((String)(mll.currentValue())).equals( "perl" )) )
        {
            mll.next();
        }
        String temp = (String)(mll.get());
        System.out.println( temp );
        System.out.println( mll );
    }
}

Hope this helps,
-Nate

[Ronald Pruitt]

Yes thank you both, you see I have an instructor that is very vague as to what he expects. Others have called him sadistic but I'm inclined to believe that sometimes those that can do can't teach and visa versa. I don't think he was meant to teach.
Thanks again.

[Peter Tran]

Or he's probably getting the students to write these programs, so he can cut-n-paste them into his new JAVA book.

[Val Dra]

i can post a code for that i did once ago , which i must say is not good but it worked , it was one of the first assignments i had done. Some teachers might know stuff but don't know how to present it to the students. In my school i have this great guy with only 3 years of field experience this guy is great , you won't even have to take notes he explains everything very well so you wouldn't second guess it. Too bad i didn't attend his class when he covered OOP stuff

[Val Dra]

this is my version of linked list don't laugh now
<code>
import java.util.NoSuchElementException;
public class ListTest {
private Node start,end,data,cursor;
private Object next,previouse;
private static int size;
protected final Object START = start;
protected final Object END = end;
private class Node {
private Node next;
private Node previouse;
private Object data;
private void setNext( Object o ) {
next = ( Node )o;
}
private void setPreviouse( Object o ) {
previouse = ( Node )o;
}
private void setData( Object o ) {
data = o;
}
private Node getNext() { return next;}
private Node getPreviouse() { return previouse;}
private Object getData() { return data;}
}
public void addElement( Object o ) {
if ( isEmpty() ) {
start = end = new Node();
start.setData( o );
}
else {
Node temp = end;
end = new Node();
setCursor( temp );
getCursor().setNext( end );
end.setPreviouse( temp );
}
end.setData( o );
setCursor( end );
size++;
}
private void setCursor( Node current ) { cursor = current; }
private Node getCursor() { return cursor; }
public boolean isEmpty() { return getSize() == 0; }
public Object getLast() { return end.getData(); }
public Object getFirst() { return start.getData(); }
public Object previouseElement() throws NoSuchElementException {
if ( getSize() == 0 ) throw new NoSuchElementException(
"No Previouse Record");
if ( getCursor().getPreviouse() == null )
setCursor( end );
else
setCursor( getCursor().getPreviouse() );
return getCursor().getData();
}
public Object nextElement() throws NoSuchElementException {
if ( getSize() == 0 ) throw new NoSuchElementException(
"No Next Record");
if ( getCursor().getNext() == null )
setCursor( start );
else
setCursor( getCursor().getNext() );
return getCursor().getData();
}
public void reset( Object pos ) throws NoSuchElementException {
if ( getCursor() == null ) throw new NoSuchElementException(
"No Record");
setCursor( ( Node )pos );
}
public boolean hasMoreElements() {
return getCursor().getNext() != null;
}
public void remove() throws NoSuchElementException {
if ( getCursor() == null ) throw new NoSuchElementException(
"No Records");
if ( ( getCursor().getPreviouse() != null ) && ( getCursor().getNext() != null ) ) {
Node prev = getCursor().getPreviouse();
Node next = getCursor().getNext();
next.setPreviouse( prev );
prev.setNext( next );
setCursor( next );
}
else {
if ( getCursor().getPreviouse() == null && getSize() > 1) {
start = getCursor().getNext();
start.setPreviouse( null );
setCursor( start );
}
else if ( getCursor().getNext() == null && getSize() > 1) {
end = getCursor().getPreviouse();
end.setNext( null );
setCursor( end );
}
else
start = end = cursor = null;
}
size--;
}
public Object currentElement() throws NoSuchElementException {
if ( getCursor() == null ) throw new NoSuchElementException(
"No Corrent Element");
return getCursor().getData();
}
public int getSize() {
return size;
}
}
</code>