feat: add java Code

Author: azl397985856

problems/206.reverse-linked-list.md

@@ -25,39 +25,11 @@ A linked list can be reversed either iteratively or recursively. Could you imple
 
 ## 代码
 
-语言支持：JS, C++, Python
+语言支持：JS, C++, Python,Java
 
 JavaScript Code：
 
 ```js
-/*
- * @lc app=leetcode id=206 lang=javascript
- *
- * [206] Reverse Linked List
- *
- * https://leetcode.com/problems/reverse-linked-list/description/
- *
- * algorithms
- * Easy (52.95%)
- * Total Accepted:    532.6K
- * Total Submissions: 1M
- * Testcase Example:  '[1,2,3,4,5]'
- *
- * Reverse a singly linked list.
- *
- * Example:
- *
- *
- * Input: 1->2->3->4->5->NULL
- * Output: 5->4->3->2->1->NULL
- *
- *
- * Follow up:
- *
- * A linked list can be reversed either iteratively or recursively. Could you
- * implement both?
- *
- */
 /**
  * Definition for singly-linked list.
  * function ListNode(val) {
@@ -134,6 +106,33 @@ class Solution:
         return prev
 ```
 
+Java Code:
+
+```java
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public ListNode reverseList(ListNode head) {
+        ListNode pre = null, cur = head;
+
+        while (cur != null) {
+            ListNode next = cur.next;
+            cur.next = pre;
+            pre = cur;
+            cur = next;
+        }
+
+        return pre;
+    }
+}
+```
+
 ## 拓展
 
 通过单链表的定义可以得知，单链表也是递归结构，因此，也可以使用递归的方式来进行reverse操作。