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Thread: List problems

  1. #1
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    Default List problems

    I am right now reading a Java course. And I have totally get stucked with one of my task.
    My task is that I am trying to make a list that i can add and get object from.
    I have an API I build my list from, so the methods and the constructor in my classes have to be there. The problem come when I am trying to add some objects to the list. When I am trying to add an object, I only get back null object. And I have no ide what the problem is. I would be really happy if someone please could told me what I am doing wrong.



    import java.lang.Object.*;
    public class Node {
        Object item;
        Node next;
        public Node (java.lang.Object newItem) 
        {
            setItem(newItem);
            setNext(null);
        }
     
        public Node(java.lang.Object newItem, Node nextNode)
        {
            setItem(newItem);
            setNext(nextNode);
        }
     
        public void setItem (java.lang.Object newItem)
        {
           item = newItem;
        }
     
        public java.lang.Object getItem()
        {
            return item;
        }
     
        public void setNext(Node nextNode)
        {
            next = nextNode;
        }
     
        public Node getNext()
        {
            return next;
        }
     
    }

    import java.lang.Object.*;
    public class ListReferencedBased implements ListInterface{
        int numItems;
        Node head;
     
        private Node find (int index)
        {
         Node current = head;
         if (index >= numItems)
         {
           return null;
         }
         else
         {
          for (int count=0; count<index; count++)
          {
          current = current.getNext();
          }
          return current;
         }
         }        
     
        public ListReferencedBased()
        {
            head = null;
            numItems = 0;
        }
     
        @Override
        public void add(int index, Object item) throws ListIndexOutOfBoundsException {
            Node pre, cur;
             if (index < 1 || index > numItems+1)
             {
                 numItems++;
             }    
                if (isEmpty()) {
     
                head = new Node(item);
                numItems++;
                }
                else{
                    head = new Node(find(index), head);
                    numItems++;
              }
     
      /*      pre = find(index-1);
            cur = pre.getNext();
            pre.setNext(new Node(item, cur));
        */    
        }
     
        @Override
        public Object get(int index) throws ListIndexOutOfBoundsException {
           head.setNext(find(index));
           if(find(index) != null)
           {    
           return head.getItem();
           }else{
           return null;
           } 
        }
     
        @Override
        public boolean isEmpty() {
            if(numItems == 0) 
            {
            return true;
            }
            else
            {    
            return false;    
            }
        }
     
        @Override
        public void remove(int index) throws ListIndexOutOfBoundsException {
            throw new UnsupportedOperationException("Not supported yet.");
        }
     
        @Override
        public void removeAll() {
          head.next = null;  
        }
     
         @Override
        public int size() {
      /*    numItems=0;
            while(head!=null)
            {
                numItems++;
                head.getNext();
            }*/
        return numItems;  
        }
    }


  2. #2
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    Default Re: List problems

    You have marked this thread as solved. Does that mean you figured this out?
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