java Iterator双向迭代输出

 1 package test;
 2 
 3 import java.util.ArrayList;
 4 import java.util.List;
 5 import java.util.ListIterator;
 6 import java.util.SortedSet;
 7 import java.util.TreeSet;
 8 
 9 public class test {
10     public static void main(String[] args)  {
11         List<String> all=new ArrayList<String>();
12         all.add("hello");
13         all.add("_");
14         all.add("World");
15         ListIterator<String> iter=all.listIterator();
16         while(iter.hasNext()){
17             System.out.print(iter.next());
18         }
19         while(iter.hasPrevious()){
20             System.out.print(iter.previous());
21         }
22     }
23 }