如何在Java中创建链接列表数据结构？

public class ListNode {
    int val;
    ListNode next;

    public ListNode(int val) {
        this.val = val;
        this.next = null;
    }
}

public class LinkedList {
    private ListNode head;

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

    // 添加元素到链表末尾
    public void add(int val) {
        if (head == null) {
            head = new ListNode(val);
            return;
        }

        ListNode current = head;
        while (current.next != null) {
            current = current.next;
        }
        current.next = new ListNode(val);
    }

    // 打印链表
    public void print() {
        ListNode current = head;
        while (current != null) {
            System.out.print(current.val + " -> ");
            current = current.next;
        }
        System.out.println("null");
    }
}

public class Main {
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.add(1);
        list.add(2);
        list.add(3);
        list.print(); // 输出：1 -> 2 -> 3 -> null
    }
}