Data Structures, Algorithms, & Applications in Java
Chapter 5, Exercise 19

/** shift elements left by amountOfShift
  * @throws IllegalArgumentException when amountOfShift < 0 */
public void leftShift(int amountOfShift)
{
   // empty list is easily shifted by any amount
   if (size == 0)
      return;

   // validate shift amount
   if (amountOfShift < 0)
      throw new IllegalArgumentException("shift amount must be >= 0,"
                       + " you have specified " + amountOfShift);

   int newSize = 0;
   if (amountOfShift < size)
   {// at least one element remains
      newSize = size - amountOfShift;
      System.arraycopy(element, amountOfShift, element, 0, newSize);
   }

   // set size and replace vacated slots with null
   while (size != newSize)
      element[--size] = null;   // enable garbage collection
}