面试题16：反转链表

package offer;
public class  {
	static class ListNode{
		int data;
		ListNode  next;
	}
	 public ListNode ReverseList(ListNode head){  
	        if(head == null)  
	            return null;  
	        ListNode preListNode = null;  
	        ListNode nowListNode = head;  
	          
	        while(nowListNode != null){  
	            ListNode nextListNode = nowListNode.next;   
	            nowListNode.next = preListNode;             //当前结点指向前一个结点  
	            preListNode = nowListNode;                  //前任结点 到现任节点  
	            nowListNode = nextListNode;                 //现任节点到下一结点  
	        }  
	        return preListNode;  
	    }  
	 public static void main(String[] args){  
	        ListNode head = new ListNode();  
	        ListNode second = new ListNode();  
	        ListNode third = new ListNode();  
	        ListNode forth = new ListNode();  
	        head.next = second;  
	        second.next = third;  
	        third.next = forth;  
	        head.data = 1;  
	        second.data = 2;  
	        third.data = 3;  
	        forth.data = 4;  
	        t16 test = new t16();  
	        ListNode result = test.ReverseList(head);  
	        System.out.println(result.data);  
	 }
}