/** * ArrayList.add(int index, E element) */
public void add(int index, E element) {
	rangeCheckForAdd(index);
	ensureCapacityInternal(size + 1);
	// 数组拷贝
	System.arraycopy(elementData, index, elementData, index + 1,
	                 size - index);
	elementData[index] = element;
	size++;
}

// System类的本地方法
public static native void arraycopy(Object src,  int  srcPos,
                                        Object dest, int destPos,
                                        int length);