如何判断单链表是否有环

@Data
public class Node {
    
    private Object data;
    
    private Node next;

    public Node(Object data) {
        this.data = data;
    }

    public Node(Object data, Node next) {
        this.data = data;
        this.next = next;
    }
}

package day04;


public class Test05 {
    public static void main(String[] args) {
        //创建一个单链表
        Node lastNode = new Node(55);
        Node node4 = new Node(44,lastNode);
        Node node3 = new Node(33,node4);
        Node node2 = new Node(22,node3);
        Node headNode = new Node(11,node2);
        lastNode.setNext(node3);
        //测试单链表是否有环
        boolean flag = isCycle(headNode);
        System.out.println(flag);
    }

    
    public static boolean isCycle(Node headNode){
        //处理headNode为null的情况
        if (headNode == null)
            return false;
        //定义一个快指针，每次往后走两步
        Node fast = headNode;
        //定义一个慢指针，每次往后走一步
        Node slow = headNode;
        //定义一个循环，用于判断单链表是否有环
        while (fast != null && fast.getNext() != null){
            //设置快指针和慢指针每次往后移动
            fast = fast.getNext().getNext();
            slow = slow.getNext();
            //如果fast和slow指向的是同一个节点，则证明单链表有环
            if (fast == slow)
                return true;
        }
        //执行到此处，证明单链表是无环单链表
        return false;
    }
}