为什么ArrayList每次扩容1.5倍

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!! // add一个元素时，size + 1
    elementData[size++] = e;
    return true;
}

private void ensureCapacityInternal(int minCapacity) {
    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity)); 
}

private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

    // overflow-conscious code
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}

private static int calculateCapacity(Object[] elementData, int minCapacity) { // 计算新容量
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) { // 代表elementData数组还是一个空数组，没有任何数据
        return Math.max(DEFAULT_CAPACITY, minCapacity); // elementData为空时，会扩容到DEFAULT_CAPACITY = 10和minCapacity的最大值，而minCapacity在插入数据时第一次值为1（size + 1 = 1），会扩容为10
    }
    return minCapacity;
}

/**
* 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);
}

private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0) // overflow
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
    MAX_ARRAY_SIZE;
}

// 新容量计算
int newCapacity = oldCapacity + (oldCapacity >> 1);