双向链接列表在列表的开头和结尾均带有空对象

Question

I was trying to create a doubly linked list with null objects at the beginnig and end of the list. What does null objects means at the beginning and end of the list. Does creating firstNode =null and lastNode == null will solve this problem or it means something different? Any suggestions will be appreciated.

// Creating a doubly linked list.
    doubleLinkedList = new DoubleLinkedList();

class DoubleLinkedList {

    private NewLink firstNode;
    private NewLink lastNode;
    private NewLink rootNode;

    // Initializing values in the Constructor for DoubleLinkedList
    public DoubleLinkedList() {

        rootNode  = null;
        firstNode = null;
        lastNode  = null;

    }

}



class NewLink {

    public String  data;
    public NewLink nextPointer;
    public NewLink previousPointer;

    public NewLink(String id) {

        data = id;

    }

    // Overriding toString method to return the actual data of the node
    public String toString() {

        return "{" + data + "} ";

    }
}

Answer 1

You didn't provide enough information to determine if you were using the standard "LinkedList" collection, or implementing your own. You also didn't give any idea exactly what you're trying to do, or what's going wrong.

ANYWAY:

Assuming you're interested in the standard LinkedList, here are some good tutorials:

• http://java.sun.com/developer/onlineTraining/collections/Collection.html

• http://java.sun.com/developer/onlineTraining/collections/Collection.html#ArrayListLinkedListClasses

• http://www.dreamincode.net/forums/topic/143089-linked-list-tutorial/

And to your specific question: No. There's seldom any need to explicitly set anything to "null". Just create your container list, add stuff to it, and perform operations on the list items.