JAVA 双向链表

在Java中实现双向链表需要定义一个节点类，节点类中包含一个数据项和两个指针，分别指向前一个节点和后一个节点。下面是一个简单的Java代码示例：

class Node {
    int data;
    Node prev;
    Node next;

    public Node(int data) {
        this.data = data;
        this.prev = null;
        this.next = null;
    }
}

class DoublyLinkedList {
    Node head;

    public DoublyLinkedList() {
        this.head = null;
    }

    // 在链表头部插入一个节点
    public void insertAtHead(int data) {
        Node newNode = new Node(data);
        newNode.next = head;

        if (head != null) {
            head.prev = newNode;
        }

        head = newNode;
    }

    // 在链表尾部插入一个节点
    public void insertAtTail(int data) {
        Node newNode = new Node(data);

        if (head == null) {
            head = newNode;
            return;
        }

        Node current = head;
        while (current.next != null) {
            current = current.next;
        }

        current.next = newNode;
        newNode.prev = current;
    }

    // 在指定位置插入一个节点
    public void insertAtPosition(int data, int position) {
        Node newNode = new Node(data);

        if (head == null || position == 1) {
            newNode.next = head;

            if (head != null) {
                head.prev = newNode;
            }

            head = newNode;
            return;
        }

        Node current = head;
        int currentPosition = 1;

        while (currentPosition < position - 1 && current.next != null) {
            current = current.next;
            currentPosition++;
        }

        newNode.next = current.next;        newNode.prev = current;
        current.next = newNode;

        if (newNode.next != null) {
            newNode.next.prev = newNode;
        }
    }

    // 从链表中删除一个节点
    public void deleteNode(int data) {
        if (head == null) {
            return;
        }

        Node current = head;

        while (current != null) {
            if (current.data == data) {
                if (current.prev != null) {
                    current.prev.next = current.next;
                } else {
                    head = current.next;
                }

                if (current.next != null) {
                    current.next.prev = current.prev;
                }

                return;
            }

            current = current.next;
        }
    }

    // 输出链表中的所有节点
    public void display() {
        Node current = head;

        while (current != null) {
            System.out.print(current.data + " ");
            current = current.next;
        }

        System.out.println();
    }
}

然后可以通过以下方式进行测试：

public class Main {
    public static void main(String[] args) {
        DoublyLinkedList list = new DoublyLinkedList();

        list.insertAtHead(3);
        list.insertAtHead(2);
        list.insertAtHead(1);

        list.insertAtTail(4);
        list.insertAtTail(5);

        list.insertAtPosition(6, 3);

        list.display(); // 输出：1 2 6 3 4 5

        list.deleteNode(3);

        list.display(); // 输出：1 2 6 4 5
    }
}