java源码分析(12)-ConcurrentModificationException

public static void main(String[] args) {
ArrayList<Integer> list=new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
Iterator<Integer> iterator=list.iterator();
while(iterator.hasNext()){
Integer i=iterator.next();
if(i==1){
list.remove(i);
}
}

}

</pre><pre name="code" class="java">public Iterator<E> iterator() {
return new Itr();
}
private class Itr implements Iterator<E> {
int cursor; //迭代器next指向的下标
int lastRet = -1; //现在指向的下标
int expectedModCount = modCount;//modCount为AbstractList中定义的属性，用于记录list被更改

的次数
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();//用于确认容器的属性是否发生变化（未通知迭代器的属性改变）
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}

public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();

try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;//可以看到迭代器中的remove方法在移除元素后，还将修改后的modCount通知了迭代器，使迭代过程中的list属性保持一致
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}

final void checkForComodification() {
if (modCount != expectedModCount)//判断有效性，在迭代过程中，若出现非迭代器更改list的情况，将会抛异常以此来保证list属性的一致性
throw new ConcurrentModificationException();
}
}

public static void main(String[] args) {
ArrayList<Integer> list=new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);
Iterator<Integer> iterator=list.iterator();
while(iterator.hasNext()){
Integer i=iterator.next();
if(i==1){
iterator.remove();
}
}

}