ArrayList是如何实现的，ArrayList和LinedList的区别？ArrayList如何实现扩容。

ArrayList比较简单，主要是通过数组来实现的
需要注意的是其初始容量是10
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
需要注意增长方法grow()

/**
* Increases the capacity to ensure that it can hold at least the
* number of elements specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
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);
}

只要size > 数组的长度，就会触发grow，其中增长比例是原来的容量的一半
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
然后把原来数组的内容拷贝到新的数组

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ArrayList和LinkedList的区别
ArrayList是通过数组来实现的，读取性能很高，随机访问时间复杂度为O(1)，适用于读大于写的场景
LinkedList是是通过双向队列来实现的，更新效率更高，写只需要修改前后两个节点的相关引用，但是读取效率比较低，需要最多遍历一半长度的队列，适用与写大于读的场景