• HashMap、arralist、linkedlist、vector不允許通過Iterator遍歷的同時修改，而ConcurrentHashMap允許該行為，並且該更新對後續的遍歷可見

• public class Qiao {
      public static class T1 extends Thread
      {
          private List<Integer> list;
  
          public T1(List<Integer> list)
          {
              this.list = list;
          }
  
          public void 
   
  run()
          {
              for (Integer i : list)
              {
              }
          }
      }
  
      public static class T2 extends Thread
      {
          private List<Integer> list;
  
          public T2(List<Integer> list)
          {
              this.list = list;
          }
  
          public void 
   
  run()
          {
              for (int i = 0; i < list.size(); i++)
              {
                  list.remove(i);
              }
          }
      }
      public static void main(String[] args)
      {
          List<Integer> list = new Vector<Integer>();
  
          for (int i = 0; i < 10000; i++)
          {
              list.add(i);
          }
  
          T1 t1 = new 
   
  T1(list);
          T2 t2 = new T2(list);
          t1.start();
          t2.start();
      }
  }
  

  結果：
  Exception in thread "Thread-0" java.util.ConcurrentModificationException
  at java.util.Vector$Itr.checkForComodification(Vector.java:1184)
  at java.util.Vector$Itr.next(Vector.java:1137)
  at cn.quantgroup.pinjamancepat.controller.Qiao$T1.run(Qiao.java:19)
  
  
  Process finished with exit code 0
  

public class Qiao2 {
    public static class T1 extends Thread {
        private Map map;

        public T1(Map map) {
            this.map = map;
        }

        public void run() {
            for (Object a : map.entrySet()) {
            }
        }
    }

    public static class T2 extends Thread {
        private Map map;

        public T2(Map map) {
            this.map = map;
        }

        public void run() {
            for (Object a : map.keySet()) {
                map.remove(a);
            }
        }
    }

    public static void main(String[] args) {
        Map map = new ConcurrentHashMap();

        for (int i = 0; i < 10000; i++) {
            map.put(i, i + 1);
        }

        T1 t1 = new T1(map);
        T2 t2 = new T2(map);
        t1.start();
        t2.start();
    }
}

結果：Process finished with exit code 0