public class FailFastTest { 
 private static List<Integer> list = new ArrayList<>(); 
  
 /** 
  * @desc:线程one迭代list 
  * @Project:test 
  * @file:FailFastTest.java 
  * @Authro:chenssy 

  */ 
 private static class threadOne extends Thread{ 
  public void run() { 
   Iterator<Integer> iterator = list.iterator(); 
   while(iterator.hasNext()){ 
    int i = iterator.next(); 
    System.out.println("ThreadOne 遍历:" + i); 
    try { 
     Thread.sleep(10); 
    } catch (InterruptedException e) { 
     e.printStackTrace(); 
    } 
   } 
  } 
 } 
  
 /** 
  * @desc:当i == 3时，修改list 
  * @Project:test 
  * @file:FailFastTest.java 
  * @Authro:chenssy 
  * @data:2014年7月26日 
  */ 
 private static class threadTwo extends Thread{ 
  public void run(){ 
   int i = 0 ; 
   while(i < 6){ 
    System.out.println("ThreadTwo run：" + i); 
    if(i == 3){ 
     list.remove(i); 
    } 
    i++; 
   } 
  } 
 } 
  
 public static void main(String[] args) { 
  for(int i = 0 ; i < 10;i++){ 
   list.add(i); 
  } 
  new threadOne().start(); 
  new threadTwo().start(); 
 } 
} 

ThreadOne 遍历:0 
ThreadTwo run：0 
ThreadTwo run：1 
ThreadTwo run：2 
ThreadTwo run：3 
ThreadTwo run：4 
ThreadTwo run：5 
Exception in thread "Thread-0" java.util.ConcurrentModificationException 
 at java.util.ArrayList$Itr.checkForComodification(Unknown Source) 
 at java.util.ArrayList$Itr.next(Unknown Source) 
 at test.ArrayListTest$threadOne.run(ArrayListTest.java:23) 

private class Itr implements Iterator<E> { 
  int cursor; 
  int lastRet = -1; 
  int expectedModCount = ArrayList.this.modCount; 
 
  public boolean hasNext() { 
   return (this.cursor != ArrayList.this.size); 
  } 
 
  public E next() { 
   checkForComodification(); 
   /** 省略此处代码 */ 
  } 
 
  public void remove() { 
   if (this.lastRet < 0) 
    throw new IllegalStateException(); 
   checkForComodification(); 
   /** 省略此处代码 */ 
  } 
 
  final void checkForComodification() { 
   if (ArrayList.this.modCount == this.expectedModCount) 
    return; 
   throw new ConcurrentModificationException(); 
  } 
 } 

public boolean add(E paramE) { 
 ensureCapacityInternal(this.size + 1); 
 /** 省略此处代码 */ 
} 
 
private void ensureCapacityInternal(int paramInt) { 
 if (this.elementData == EMPTY_ELEMENTDATA) 
  paramInt = Math.max(10, paramInt); 
 ensureExplicitCapacity(paramInt); 
} 
 
private void ensureExplicitCapacity(int paramInt) { 
 this.modCount += 1; //修改modCount 
 /** 省略此处代码 */ 
} 
 
ublic boolean remove(Object paramObject) { 
 int i; 
 if (paramObject == null) 
  for (i = 0; i < this.size; ++i) { 
   if (this.elementData[i] != null) 
    continue; 
   fastRemove(i); 
   return true; 
  } 
 else 
  for (i = 0; i < this.size; ++i) { 
   if (!(paramObject.equals(this.elementData[i]))) 
    continue; 
   fastRemove(i); 
   return true; 
  } 
 return false; 
} 
 
private void fastRemove(int paramInt) { 
 this.modCount += 1; //修改modCount 
 /** 省略此处代码 */ 
} 
 
public void clear() { 
 this.modCount += 1; //修改modCount 
 /** 省略此处代码 */ 
} 

private static class COWIterator<E> implements ListIterator<E> { 
  /** 省略此处代码 */ 
  public E next() { 
   if (!(hasNext())) 
    throw new NoSuchElementException(); 
   return this.snapshot[(this.cursor++)]; 
  } 
 
  /** 省略此处代码 */ 
 } 

public boolean add(E paramE) { 
  ReentrantLock localReentrantLock = this.lock; 
  localReentrantLock.lock(); 
  try { 
   Object[] arrayOfObject1 = getArray(); 
   int i = arrayOfObject1.length; 
   Object[] arrayOfObject2 = Arrays.copyOf(arrayOfObject1, i + 1); 
   arrayOfObject2[i] = paramE; 
   setArray(arrayOfObject2); 
   int j = 1; 
   return j; 
  } finally { 
   localReentrantLock.unlock(); 
  } 
 } 
 
  
 final void setArray(Object[] paramArrayOfObject) { 
  this.array = paramArrayOfObject; 
 } 

Object[] arrayOfObject2 = Arrays.copyOf(arrayOfObject1, i + 1); 
arrayOfObject2[i] = paramE; 
setArray(arrayOfObject2);