这段代码是否在Arraylist.remove（int index）的源代码中是不必要的？

Question

Here's the source code:

Removes the element at the specified position in this list. Shifts any subsequent elements to the left (subtracts one from their indices). Parameters: index the index of the element to be removed Returns: the element that was removed from the list Throws: java.lang.IndexOutOfBoundsException

public E remove(int index) {
    rangeCheck(index);
    modCount++;
    E oldValue = elementData(index);
    int numMoved = size - index - 1;
    if (numMoved > 0)
    System.arraycopy(elementData, index+1, elementData, index,
        numMoved);
    elementData[--size] = null; // Let gc do its work
    return oldValue;
}

My question is:

As the rangeCheck(index) has already guarantee that index < size , is it necessary to check that if (numMoved > 0) ?

Answer 1

numMoved can be 0 (if you remove the last element by calling list.remove(list.size()-1) ), in which case no arraycopy is required. Therefore the if (numMoved > 0) is necessary.

Answer 2

删除列表的最后一个元素时， index等于size - 1 ，在这种情况下numMoved为0且不需要System.arraycopy 。