class ListNode{    public Eight data;    public ListNode next;    public ListNode()    {    	next=null;    }    public ListNode(Eight o)    {        data=o;        next=null;    }    public ListNode(Eight o,ListNode nextNode)    {        data=o;        next=nextNode;    }        // Return the Eight in this node    public Eight getEight()    {        return data;    }        public ListNode getnext()    {        return next;    }}     public class List{    public ListNode firstNode;    public ListNode lastNode;    public int length;    private String name;         //    String like "list" used in printing            public List(String s)    {        name=s;        firstNode=lastNode=null;        length=0;    }            //Constructor: Constructor an empty List with "List" as the name    public List(){        this("list");    }    public  Eight getFirstNode(){    	return firstNode.data;        }        //Insert an Eight at the front of the List If List is empty, firstNode    //and lastNode refer to same Eight. Otherwise,firstNode refers to new node.    public void insertAtFront(Eight insertItem)    {        if(isEmpty())//如果鏈表為空,返回true,否則返回false.            firstNode=lastNode=new ListNode(insertItem);        else            firstNode=new ListNode(insertItem,firstNode);        length++;    }            //Insert an Eight at the end of the List If List is empty, firstNode and    //lastNode refer to same Eight. Otherwise, lastNode's next instance variable refers to new node.    public void insertAtBack(Eight insertItem)    {        if(isEmpty())            firstNode=lastNode=new ListNode(insertItem);        else            lastNode=lastNode.next=new ListNode(insertItem);        length++;    }        // Remove the first node from the List.    public Eight removeFromFront() throws EmptyListException    {        Eight removeItem=null;        if(isEmpty())            throw new EmptyListException(name);                removeItem=firstNode.data;   //retrieve the data reset the firstNode and lastNode references                if(firstNode.equals(lastNode))            firstNode=lastNode=null;        else            firstNode=firstNode.next;        length--;        return removeItem;    }        //Remove the last node from the List    public Eight removeFromBack() throws EmptyListException    {        Eight removeItem=null;                if(isEmpty())            throw new EmptyListException(name);                removeItem=lastNode.data; //retrieve the data reset the firstNode and lastNode references        if(firstNode.equals(lastNode))            firstNode=lastNode=null;        else        {            ListNode current=firstNode;                    while(current.next !=lastNode){                current=current.next;            }                    lastNode=current;            current.next=null;        }        length--;        return removeItem;    }        //Return true if the List is empty.    public boolean isEmpty(){        return firstNode==null;    }        //Output the List contents    public void print()    {    	if(isEmpty()){            System.out.println("Empty ");            return;        }    	ListNode current=firstNode;    	do    	{            current.data.print();            System.out.println("f??:"+current.data.f());            System.out.println("=====");            current=current.next;        }while(current !=null);            } }     // Class EmptyListException definitionclass EmptyListException extends RuntimeException{    public EmptyListException(String name)    {        super("The " + name + " is empty");    }}