Is this snippet unnecessary in the source code of Arraylist.remove(int index)?

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)?

Eran · Accepted Answer · 2015-11-17 12:33:03Z

6

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.

answered Nov 17, 2015 at 12:33

Eran

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Niels Billen · Accepted Answer · 2015-11-17 12:42:07Z

5

When you remove the last element of the list, index is equal to size - 1, in which case numMoved is 0 and no System.arraycopy is required.

edited Nov 17, 2015 at 12:42

answered Nov 17, 2015 at 12:33

Niels Billen

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