public boolean add(E e) {
     ensureCapacity(size + 1);  // 增加元素，判斷是否能夠容納。不能的話就要新建數組
     elementData[size++] = e;
     return true;
 }
  public void ensureCapacity(int minCapacity) {
     modCount++;
     int oldCapacity = elementData.length;
     if (minCapacity > oldCapacity) {
         Object oldData[] = elementData; // 此行沒看出來用處，不知道開發者出于什么考慮
         int newCapacity = (oldCapacity * 3)/2 + 1; // 增加新的數組的大小
         if (newCapacity < minCapacity)
        newCapacity = minCapacity;
             // minCapacity is usually close to size, so this is a win:
             elementData = Arrays.copyOf(elementData, newCapacity);
     }
 }

private void ensureCapacityHelper(int minCapacity) {
     int oldCapacity = elementData.length;
     if (minCapacity > oldCapacity) {
         Object[] oldData = elementData;
         int newCapacity = (capacityIncrement > 0) ?
        (oldCapacity + capacityIncrement) : (oldCapacity * 2);
         if (newCapacity < minCapacity) {
        newCapacity = minCapacity;
         }
        elementData = Arrays.copyOf(elementData, newCapacity);
     }
 }