.ArrayList是如何实现的，ArrayList和LinkedList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