List的add方法

用了很久的List的add方法，偶然间才知道还有一个add(int index, E element) 方法，在指定的位置插入元素，此方法可以巧妙的用于给需要构建的的list倒序。

List接口中的这两个add方法：

• boolean add(E e);
• void add(int index, E element);

jdk源码中的两个add方法：

/**
 * Appends the specified element to the end of this list.
 *
 * @param e element to be appended to this list
 * @return true (as specified by {@link Collection#add})
 */
public boolean add(E e)
{
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}

/**
 * Inserts the specified element at the specified position in this
 * list. Shifts the element currently at that position (if any) and
 * any subsequent elements to the right (adds one to their indices).
 *
 * @param index index at which the specified element is to be inserted
 * @param element element to be inserted
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public void add(int index, E element)
{
    rangeCheckForAdd(index);

    ensureCapacityInternal(size + 1);  // Increments modCount!!
    System.arraycopy(elementData, index, elementData, index + 1,
                     size - index);
    elementData[index] = element;
    size++;
}