java链表寻找中间节点

public class ListNode {    public int info;    public ListNode next;//这里就是链接，指向下一个节点的内存地址    ListNode first, last, newNode;    public ListNode buildList(int[] input) {        if (input.length > 0) {            for (int i = 0; i < input.length; i++) {                newNode = new ListNode();                newNode.info = input[i];                newNode.next = null;                if (first == null) {                    first = newNode;                    last = newNode;                } else {                    last.next = newNode;                    last = newNode;                }            }        }        return first;    }    public static void main(String[] args) {        int[] array = {1, 2, 3, 4};        ListNode linkedList = new ListNode();        ListNode head = linkedList.buildList(array);        ListNode.printList(head);        findMid(head);    }    private static void printList(ListNode head) {        while (head != null) {            System.out.println(head.info);            head = head.next;        }    }    private static void findMid(ListNode head) {        ListNode slow = head;        ListNode fast = head;        while (fast !=null && fast.next !=null )        {            fast = fast.next.next;            slow = slow.next;        }//这个总数是4，会取3        //这个方法也可以//        while(fast.next != null){//            if(fast.next.next != null){//                fast = fast.next.next;//                slow = slow.next;//            } else {////                fast = fast.next;//                break;//这个地方就退出循环了，用break或者fast = fast.next;都可以//            }////        }        System.out.println(slow.info);    }}