ArrayList集合在底层添加元素时,会创键一个默认长度为10的数组,我看源码只是声明了一个elementData的数组,并没有指定数组的长度,
看源码到是有个常量10,但不知到在哪里为数组长度赋的值
java.util.ArrayList#grow这个方法的最后一句进行了扩容和拷贝
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
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);
}