Java 迭代器

1.快速报错

 public class FailFast {
       public static void main(String[] args) {
             List<String> c = new ArrayList<String>();
             Iterator<String> it = c.iterator();
             c.add("An object");
             String s = it.next();  // java.util.ConcurrentModificationException
      }
 }

在取得迭代器之后，Java采用快速报错机制防止多个线程同时修改同一个容器的内容，而不是在事后来检查问题。

2.在容器中查找满足条件的元素，并将之删除

     public  static void main(String[] args) {
         HashSet hs=new HashSet();
         hs.add("mm");
         hs.add("kk");
         hs.add("ss");
         Iterator itor=hs.iterator();

         while(itor.hasNext()){
             String c=(String)itor.next();
             if(c=="kk"){
                 itor.remove();
             }
         }

        System.out.println(hs.toString());

     }

3.多种实现

 class ReversibleArrayList<T> extends ArrayList<T> {
     public ReversibleArrayList(Collection<T> c) {
         super(c);
     }

     public Iterable<T> reversed() {
              return new Iterable<T>() {
                       public Iterator<T> iterator() {
                             return new Iterator<T>() {
                                   int current = size() - 1;
                                   public boolean hasNext() {
                                       return current > -1;
                                   }
                                   public T next() {
                                       return get(current--);
                                   }
                                   public void remove() {
                                         throw new UnsupportedOperationException();
                                   }
                             };
                   }
             };
       }
 }    

 public class AdapterMethodIdiom {
     public static void main(String[] args) {
         ReversibleArrayList<String> ral = new ReversibleArrayList<String>(Arrays.asList("To be or not to be".split(" ")));
         for(String s : ral)
           System.out.print(s + " ");

         System.out.println("");

         for(String s : ral.reversed())
           System.out.print(s + " ");
   }
 }