在java中实现循环链​​表

Question

I'm having a bit of an issue with implementing my circularly linked list. I'm working on a problem that requires you to implement any ADT yourself. I seem to be okay with adding nodes to the list, however I'm in unfamiliar territory when it comes to removing. I included the first two remove methods to give you an idea of where my head is at, how would I go about removing the last node in the list?

public class LinkedList {
    private Node head;
    private Node tail;
    private int size = 0;
    LinkedList() {
        head = null;
        current = null;
        previous = null;
        tail = null;
        size = 0;
    }

    //checks if list is empty
    public boolean isEmpty() {
        return head == null;
    }
    //add new node to front of circularly linked list
    public void addToFront(E x) {
        if (head == null) {
            head = new Node(x);
        } else {
            Node n = new Node(x);
            x.next() = head;
            head = x;
        }
    }

    public void addtoMiddle(E x) {
        x.next = current.next();
        current.next = x;
        size = size + 1;
    }

    public void addToEnd(E x) {
        x.next = null;
        tail.next() = x;
        tail = x;
        size = size + 1;
    }

    public void removeFirst(E x) {
        if (head = null) {
            System.out.println("Error! List is empty!");
        } else {
            head = current.next();
            size = size + 1;
        }
    }

    public void removeMiddle(E x) {
        previous.next() = current.next();
        current.next() = null;
        size = size + 1;
    }

Answer 1

In a circular linked list the last node's next points to the head, so you loop through your nodes until node.next.equals( head ) . Note that next must never be null and if you have only one node then you have head.next = head .

In a circular doubly linked list you also have a previous node, ie you can iterate backwards. In that case your last node is just head.previous .

A small ascii picture:

head -next---> node -next---> node -next---> last
 | ^  <---prev-      <---prev-      <---prev- | ^
 | |                                          | |
 | |_____________________________________next_| |
 |_prev_________________________________________|      

Answer 2

I know this is not directly an answer to your question but I feel like Thomas has given the needed explanation here.

Since you have a lot of syntax or incompleteness errors in the example I would recommend to comment out all functions so it has no more errors. Then comment them in again one by one correcting every error.

Some advices:

You use class members which are not defined eg current , previous .

Decide if next should be a member or function.

You need to define a class for Node (containing its members and functions), like you did for LinkedList .