Java的链表类

Java的链表是一种线性数据结构，它由一系列节点组成，每个节点包含一个数据元素和一个指向下一个节点的指针，链表可以分为单向链表、双向链表和循环链表等类型。

1、单向链表

单向链表是最简单的链表类型，每个节点只有一个指向下一个节点的指针，下面是一个简单的单向链表实现：

class Node {
    int data;
    Node next;
    public Node(int data) {
        this.data = data;
        this.next = null;
    }
}
class LinkedList {
    Node head;
    public void add(int data) {
        Node newNode = new Node(data);
        if (head == null) {
            head = newNode;
        } else {
            Node current = head;
            while (current.next != null) {
                current = current.next;
            }
            current.next = newNode;
        }
    }
    public void display() {
        Node current = head;
        while (current != null) {
            System.out.print(current.data + " > ");
            current = current.next;
        }
        System.out.println("null");
    }
}

2、双向链表

双向链表与单向链表类似，但每个节点有两个指针，一个指向前一个节点，一个指向后一个节点，下面是一个简单的双向链表实现：

class DoublyNode {
    int data;
    DoublyNode prev;
    DoublyNode next;
    public DoublyNode(int data) {
        this.data = data;
        this.prev = null;
        this.next = null;
    }
}
class DoublyLinkedList {
    DoublyNode head;
    DoublyNode tail;
    public void add(int data) {
        DoublyNode newNode = new DoublyNode(data);
        if (head == null) {
            head = newNode;
            tail = newNode;
        } else {
            tail.next = newNode;
            newNode.prev = tail;
            tail = newNode;
        }
    }
    public void display() {
        DoublyNode current = head;
        while (current != null) {
            System.out.print(current.data + " <> ");
            current = current.next;
        }
        System.out.println("null");
    }
}

3、循环链表

循环链表是一种特殊的链表，它的最后一个节点的指针指向第一个节点，形成一个环，下面是一个简单的循环链表实现：

class CircularDoublyNode {
    int data;
    CircularDoublyNode prev;
    CircularDoublyNode next;
    public CircularDoublyNode(int data) {
        this.data = data;
        this.prev = null;
        this.next = null;
    }
}
class CircularDoublyLinkedList {
    CircularDoublyNode head;
    CircularDoublyNode tail;
    public void add(int data) {
        CircularDoublyNode newNode = new CircularDoublyNode(data);
        if (head == null) {
            head = newNode;
            tail = newNode;
            head.next = head; // 形成环的指针指向自己（头结点）和尾结点（头结点）的指针都指向头结点（尾结点）形成环状结构。