CopyOnWriteArrayList的理解与理解

String[] data={"a","b","c"};
		ArrayList<String> array = new ArrayList<String>();
		array.add("a");
		array.add("b");
		array.add("c");
		for(String s : array){
			System.out.println(s);
			array.remove(s);
		}

输出：Exception in thread "main" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(Unknown Source)
at java.util.ArrayList$Itr.next(Unknown Source)

反编译 字节码：

            50: invokevirtual #31                 // Method java/util/ArrayList.iterator:()Ljava/util/Iterator;
        53: astore        4
        55: goto          82
        58: aload         4
        60: invokeinterface #35,  1           // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object;
        65: checkcast     #16                 // class java/lang/String
        68: astore_3
        69: getstatic     #41                 // Field java/lang/System.out:Ljava/io/PrintStream;
        72: aload_3
        73: invokevirtual #47                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        76: aload_2
        77: aload_3
        78: invokevirtual #53                 // Method java/util/ArrayList.remove:(Ljava/lang/Object;)Z
        81: pop
        82: aload         4
        84: invokeinterface #56,  1           // InterfaceMethod java/util/Iterator.hasNext:()Z

foreach语句转化为ArrayList.iterator,在进行next()函数时抛出异常

       可用方法：

Iterator<String> iter=array.iterator();
while(iter.hasNext()){
     String s=iter.next();
     iter.remove(s);//这里的remove会调整modcount 与expectcount的关系
}

因为CopyOnWriteArrayList在做迭代之前是做了一份“快照”，所以此时的iter是不可变的，也就是说如果在此遍历中调用iter.remove();会抛出异常：java.lang.UnsupportedOperationException

public Iterator<E> iterator() {
        return new COWIterator<E>(getArray(), 0);
    }
 static final class COWIterator<E> implements ListIterator<E> {
        /** Snapshot of the array */
        private final Object[] snapshot;
        /** Index of element to be returned by subsequent call to next.  */
        private int cursor;

        private COWIterator(Object[] elements, int initialCursor) {
            cursor = initialCursor;
            snapshot = elements;
        }
public boolean hasNext() {
         return cursor < snapshot.length;
        }

        public boolean hasPrevious() {
            return cursor > 0;
        }

        @SuppressWarnings("unchecked")
        public E next() {
            if (! hasNext())
                throw new NoSuchElementException();
            return (E) snapshot[cursor++];
        }

        @SuppressWarnings("unchecked")
        public E previous() {
            if (! hasPrevious())
                throw new NoSuchElementException();
            return (E) snapshot[--cursor];
        }
...
}

办法一：使用直接方式，一边遍历，一边add/remove()，这里实现遍历与写的分离所以不会错误

for(String item : list){ 
    String tem = item + "..."; 
    list.remove(item); 
    list.add(tem); 
} 

验证连接：http://www.cnblogs.com/alipayhutu/archive/2012/08/11/2634073.html