Thread: LinkedList Objects

Hi all, I'm creating a LinkedList...I've removed most unnecessary code for simplicity. Here's what I expect to happen. I create a list opject, populate it with an item, get the size (which is 1) the I create a list2 object, populate it with an item and get the size of list again...which I would still expect to be 1, but it is 2...why is that happening? Here is my full code:

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner; //Needed for scanner class
 
/**
 * class TestLinkedList -
 */
public class TestLinkedList {
	public static void main(String[] args) throws FileNotFoundException{
		//Populate list with elements
		IntLinkedList list = new IntLinkedList();
//		list = getListFrom("project2.txt");
		//Display original list
list.addAfter(4);
		System.out.println( "The original list size is: " + list.size() + 
		" and contains the elements:");
//		displayList( list );	
		System.out.println();
		//Sort list
//		list = sortList( list ); 
		//Display the sorted list
IntLinkedList list2 = new IntLinkedList();
list2.addAfter(5);
		System.out.println( "The final list size is: " + list.size() + 
		" and contains the sorted elements:");
//		displayList( list );			
        System.exit(0);	//End Program
	}//end method main
}
 
/**
 * class IntLinkedList -
 */
class IntLinkedList{
    private static int     size; //the number of elements in the list
    private static IntNode head;
    private static IntNode tail;
    private static IntNode cursor;
    private static IntNode precursor;
    //
    //IntLinkedList
    //
    public IntLinkedList(){
    }//end IntLinkedList
    //
    //compute the number of nodes
    //
    public static int size(){
    	size = 0;
    	for ( cursor = head; cursor != null; cursor = cursor.getLink() ){
    		  size++;
    	}
    	return size;
    }//end size
    //
    //addAfter
    //
	public static void addAfter( int value ){
        if ( cursor == null ) {  // either no current element or current element is first  
            // add element to the head of the list
            head = new IntNode( value, head );
            cursor = head;
         } else {               // cursor points to the middle of the list
        	cursor.setLink( new IntNode( value, cursor.getLink()) );
            //cursor = precursor.getLink();
         }
         if ( size() == 0 )     // the list was empty and tail needs to be initialized
            tail = head;
	}
}
 
/**
 * class IntNode -
 */
class IntNode{
	//
	//Variables
	//
	private int data; //variable to store an integer value.
	private IntNode link; //variable to store an IntNode object.
	//
	//Non-default constructor to initialize the data fields
	//
	public IntNode( int initData, IntNode initLink ){
		data = initData;
		link  = initLink;
	}
	//
	//Accessor and mutator methods for data and link fields
	//
	public int getData(){
		return data;
	}
	public IntNode getLink(){
		return link;
	}
	public void setData(int newData){
		data = newData;
	}
	public void setLink(IntNode newLink){
		link = newLink;
	}
}//end class IntNode

Thanks for any help,
Mason

OK, I see that when I use the word static, the method becomes part of the class and is not independent objects. But when I remove static, I get a null pointer exception...why did that happen? Here is the complete updated code, Ignore most of it, just look at list population portion.

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner; //Needed for scanner class
 
/**
 * class TestLinkedList -
 */
public class TestLinkedList {
    //
    public static void main(String[] args) throws FileNotFoundException{
      //
      IntLinkedList list = getListFrom("project2.txt");
      System.out.println( "The original list is:" );
      System.out.println();
      //displayList( list );
//      list = sortList( list );
      System.out.println( list.size() );
 
      IntLinkedList list2 = null;
      list2.addAfter(2);
      System.out.println( list2.size() );
 
      System.out.println();
      System.out.println( "The final list is:" );
      System.out.println();
      //displayList( list );
    }//end main
    //
	//
	// getListFrom() method populates the linked list with elements
	//	
	private static IntLinkedList getListFrom(String path) throws FileNotFoundException{
		//Get file
		File file = new File(path);
		Scanner inputFile = new Scanner(file);
		IntLinkedList linkedList = null;
		//Add elements
		while (inputFile.hasNext()){
			linkedList.addAfter(Integer.parseInt(inputFile.nextLine()));
		}
		inputFile.close();
		return linkedList;
	}//end method getListFrom
	//
	// displayList() method prints the elements of the linked list
	//
//	private void displayList( IntLinkedList list ){
//		IntLinkedList.printList();
//		System.out.println();
//		System.out.println(IntLinkedList.size());
//	}//end displayList
    //
//    private static IntLinkedList mergeSortedLists(
//      IntLinkedList first,
//      IntLinkedList second
//    ){
//    }//end mergeSortedLists
    //
//    private static IntLinkedList sortList( IntLinkedList list ){
//    }//end sortList
    //
  }//end class TestIntLInkedList
 
 
 
 
 
 
 
/**
 * class IntLinkedList -
 */
class IntLinkedList{
    private int     size; //the number of elements in the list
    private IntNode head;
    private IntNode tail;
    private IntNode cursor;
    private IntNode precursor;
    //
    //IntLinkedList
    //
    public IntLinkedList(){
    	head=null;
    }//end IntLinkedList
    //
    //compute the number of nodes
    //
    public int size(){
    	size = 0;
    	for ( cursor = head; cursor != null; cursor = cursor.getLink() ){
    		  size++;
    	}
    	return size;
    }//end size
    //
    //addAfter
    //
	public void addAfter( int value ){
        if ( cursor == null ) {  // either no current element or current element is first  
            // add element to the head of the list
            head = new IntNode( value, head );
            cursor = head;
         } else {               // cursor points to the middle of the list
        	cursor.setLink( new IntNode( value, cursor.getLink()) );
            //cursor = precursor.getLink();
         }
         if ( size() == 0 )     // the list was empty and tail needs to be initialized
            tail = head;
	}
	//
    //Prints list elements
	//
    public void printList() {
    	IntNode curr = head;
        while (curr != null) {
            System.out.print(curr.getData() + " ");
            curr = curr.getLink();
        }
    }
}
 
 
 
 
 
 
 
/**
 * class IntNode -
 */
class IntNode{
	//
	//Variables
	//
	private int data; //variable to store an integer value.
	private IntNode link; //variable to store an IntNode object.
	//
	//Non-default constructor to initialize the data fields
	//
	public IntNode( int initData, IntNode initLink ){
		data = initData;
		link  = initLink;
	}
	//
	//Accessor and mutator methods for data and link fields
	//
	public int getData(){
		return data;
	}
	public IntNode getLink(){
		return link;
	}
	public void setData(int newData){
		data = newData;
	}
	public void setLink(IntNode newLink){
		link = newLink;
	}
}//end class IntNode

Originally Posted by thedolphin13

I used the # tag for code...what do you use for java to get the color?

To use java tags:
[highlight=java] and [/highlight]