java单向链表的简单实现

package com.fy.api.server.demo2;


public class LkList {
   
   private Node head;
   
   private Node current;
   
   public class Node {
      
      public int data;
      
      public Node next;
      
      public Node (int data) {
         this.data = data;
      }
      
      public void add (Node node) {
          if(head == null) {
             head = node;
             current = head;
          }
         if (current.next == null) {
            current.next = node;
         } else {
            current = current.next;
            current.add(node);
         
         }
      }
       
   }

   public void addNode (Node node) {
      if (node == null) {
         System.out.println("can't add a null element!");
         return;
      }
      current = head;
      if (head == null) {
         //System.out.println("throw null pointer exception!");
         head = node;
         return;
      }
      this.current.add(node); 
   }
   
   public void showNodes () {
      this.current = head;
      int count = 0;
      System.out.print("[");
       while(this.current!=null){
          System.out.print(count==0?this.current.data: ","+this.current.data );
          count ++;
          this.current = this.current.next;
       }
       System.out.print("]");
       System.out.println();
   }
   
   public int len () {
      this.current = head;
      if (this.current == null) {
         return 0;
      }
      
      if (this.current.next == null) {
         return 1;
      }
      int len = 1;
      while (this.current.next !=null) {
         len++;
         this.current = this.current.next;
      }
      return len;
   }
   
   public void deleteNode (int index) {
      if (index <0 || index>=this.len()) {
         System.out.println("exception outof list bounds!");
         return;
      }
      
      if (index == 0) {
          head = head.next;   
          if (head!=null) {
             current = head;
          }
      }
        
      int len = 1;
      Node tmp = head;
      while (tmp.next != null) {
         if (index == len++) {
            tmp.next = tmp.next.next;
            return;
         }
         tmp = tmp.next;
      }  
   }
     
   public static void main (String []args) {
       LkList lk = new LkList();  
       Node head = lk.new Node(1);
       lk.addNode(head);
       lk.addNode(lk.new Node(2));
       lk.addNode(lk.new Node(3));
       lk.addNode(lk.new Node(4));
       System.out.println(lk.len()); 
       lk.showNodes();
       lk.deleteNode(0);
       lk.showNodes(); 
       lk.addNode(lk.new Node(5)); 
       lk.showNodes();
       lk.deleteNode(3);;
       lk.showNodes();
       System.out.println(lk.len());
   }
     
}