如何以相反的顺序迭代LinkedList元素？

Question

我是Java Collections的新手,我怀疑为什么我不能在向后的方向上遍历链表中的元素.我将解释我做了什么,请澄清我的怀疑.

1. 我为前向迭代创建了接口迭代器,为后向迭代创建了listiterator.为什么反向迭代不起作用？

2. 我不能在同一个程序中使用iterator和listiterator接口来遍历前向和后向迭代中的一组元素吗？

   代码片段:

   import java.util.*;
   class NewClass{
   public static void main(String args[]){
     LinkedList<String> obj = new LinkedList<String>();
   
      obj.add("vino");
      obj.add("ajith");
      obj.add("praveen");
      obj.add("naveen");
   
      System.out.println(obj);
   
      System.out.println("For loop ");
      //using for loop
      for(int count=0; count < obj.size(); count++){
        System.out.println(obj.get(count));
      }
     System.out.println("For each loop ");
   
     //using foreach loop
     for(String s:obj){
        System.out.println(s);
     }
     System.out.println("Whileloop ");
   
     //using whileloop
     int count=0;
     while(obj.size() > count){
         System.out.println(obj.get(count));
       count++;
     }
     System.out.println("Forward Iterations ");
     //using iterator 
     Iterator it = obj.iterator();
     while(it.hasNext()){
        System.out.println(it.next());
     }
     ListIterator lit = obj.listIterator();
     System.out.println("Backward Iterations");
      while(lit.hasPrevious()){
       System.out.println(lit.previous());
         }
       }
    }
   

   产量

   [vino, ajith, praveen, naveen]
    For loop 
    vino
    ajith
    praveen
    naveen
   For each loop 
    vino
    ajith
    praveen
    naveen
   Whileloop 
    vino
    ajith
    praveen
    naveen
   Forward Iterations 
    vino
    ajith
    praveen
    naveen
    Backward Iterations
   

Backward Iterations的输出在哪里？请有人帮帮我.谢谢

Answer 1

我想你想要一个descendingIterator.

Iterator lit = obj.descendingIterator();
System.out.println("Backward Iterations");
while(lit.hasNext()){
  System.out.println(lit.next());
}

Answer 2

可以做到，但是需要使用方法listIterator(int index)指定要在List.

LinkedList<String> obj = new LinkedList<String>();

obj.add("vino");
obj.add("ajith");
obj.add("praveen");
obj.add("naveen");

ListIterator<String> it = obj.listIterator(obj.size());
while (it.hasPrevious())
    System.out.println(it.previous());