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 + " ");
  }
}