Arraylist作为最简单的集合,需要熟悉一点,记录一下---->这边主要是注意一下扩容和遍历的过程
请看以下代码
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
list.add("e");
list.add("f");
Iterator iterator = list.iterator();
while(iterator.hasNext()){
String str = (String) iterator.next();
if(str.equals("a")){
list.remove(str);
}else{
System.out.println(str);
}
}
}
执行结果 发生了异常!for遍历的时候进行删除和添加操作,也会出现异常!
这是因为
Iterator遍历的时候 fail-fast的检查机制
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;//每次add或remove 都会增加1(有点类似于记录改变集合数据的行为),遍历的时候初始化
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();//校验遍历的时候是否修改了记录
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];
}
final void checkForComodification() {
if (modCount != expectedModCount)//判断是否相等
throw new ConcurrentModificationException();
}
}
扩容问题,其实也很简单
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)//这边当oldCapacity大到一定程度的时候,向右移动会变成很大的负数,所以才有这个判断
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// minCapacity is usually close to size, so this is a win:
elementData = Arrays.copyOf(elementData, newCapacity);
}
简单的学习下