Fail-fast (fast failure) mechanism in Java __java

Introduced in the previous ArrayList of the expansion of the problem for the modcount operation is not described in detail, the operation of the variable in Add,remove and other operations will change. So what's the effect of this variable? An introduction to the fail-fast mechanism, a fast failure mechanism, is an error detection mechanism in the Java Collection (Collection). When the set changes in structure during the iteration of the collection, it is possible to fail-fast, that is, to throw a concurrentmodificationexception exception. The fail-fast mechanism does not guarantee that exceptions will be thrown under different steps, it is just doing its best to throw, so this mechanism is typically used only to detect bugs. The fail-fast scenario may appear in our common Java collection as a fail-fast mechanism, such as Arraylist,hashmap. Rapid failure can occur in multithreaded and single-threaded environments. 1, single-threaded environment fail-fast:arraylist occurrence Fail-fast Example: [Java]  View Plain  copy public static void main (string[] args)  {          List<String> list = new ArrayList<> ();          for  (int i = 0 ; i < 10  ; i++ )  {               List.add (i +  "");         }          iterator<string> iterator = list.iterator ();          int i = 0 ;         while ( Iterator.hasnext ())  {              if   (i == 3)  {                  &nBsp; list.remove (3);              }               system.out.println (Iterator.next ());               i ++;          }  } This code defines a ArrayList collection and uses an iterator to iterate through the process, deliberately remove an element in a step iteration, There will be fail-fast.
HashMap Occurrence Fail-fast: [Java]  View Plain  copy public static void main (string[] args)  {          Map<String, String> map = new HashMap<> ();          for  (int i = 0 ; i <  10 ; i ++ )  {               map.put (i+ "",  i+ "");         }          iterator<entry<string, string>> it = map.entryset (). Iterator ();         int i = 0;          while  (It.hasnext ())  {               if  (i == 3)  {            &Nbsp;       map.remove (3+ "");               }               entry<string, string> entry = it.next ();               system.out.println ("key= "  + entry.getkey ()  +   " and value= "  + entry.getvalue ());               i++;      }  }   The code defines a HashMap object and holds 10 key-value pairs, which, during the iterative traversal, remove an element by using the Remove method of the map, causing the concurrentmodificationexception exception to be thrown:
2. Multi-threaded environment: [Java]View plain copy public class Failfasttest {public static list<string> List = new arraylist<> ();