.ArrayList是如何實現的，ArrayList和LinkedList的區別？ArrayList如何實現擴容?

ArrayList比較簡單，主要是通過數組來實現的

需要注意的是其初始容量是10

    /**
     * Default initial capacity.
     */
    private static final int DEFAULT_CAPACITY = 10;

需要注意增長方法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 > 數組的長度，就會觸發grow，其中增長比例是原來的容量的一半

        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);

然后把原來數組的內容拷貝到新的數組

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ArrayList和LinkedList的區別

ArrayList是通過數組來實現的，讀取性能很高，隨機訪問時間復雜度為O(1)，適用於讀大於寫的場景

LinkedList是是通過雙向隊列來實現的，更新效率更高，寫只需要修改前后兩個節點的相關引用，但是讀取效率比較低，需要最多遍歷一半長度的隊列，適用與寫大於讀的場景