arraylist公共构造函数-“构造初始容量为10的空列表”-在哪里?[复制品]

这是一个优化。开发人员决定初始化 ArrayList 使用空的备份数组,并且仅当开始向 List .

添加第一个元素时(通过调用 add 它叫

ensureCapacityInternal(size + 1);

检查是否 elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA 如果是,则将容量设置为

minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);

DEFAULT_CAPACITY 是 10 .

首次向列表中添加元素时,容量将设置为10。

看到这个:

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

完整程序

步骤1:

public boolean add(E e) {
    modCount++;
    add(e, elementData, size);
    return true;
}

步骤2:

private void add(E e, Object[] elementData, int s) {
    if (s == elementData.length)
        elementData = grow();
    elementData[s] = e;
    size = s + 1;
}

步骤3,列表 grows :

private Object[] grow() {
    return grow(size + 1); // size is 0 here
}

private Object[] grow(int minCapacity) {
    return elementData = Arrays.copyOf(elementData,
                                       newCapacity(minCapacity));  // newCapacity(1) will return 10, see step 4, the elementData will have capacity 10.
}

步骤4,调用 newCapacity(1) :

private int newCapacity(int minCapacity) {
    // overflow-conscious code
    int oldCapacity = elementData.length;
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity <= 0) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
            return Math.max(DEFAULT_CAPACITY, minCapacity);   // will  return 10 here !!!!
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
        return minCapacity;
    }
    return (newCapacity - MAX_ARRAY_SIZE <= 0)
        ? newCapacity
        : hugeCapacity(minCapacity);
}