public ArrayList(Collection<? extends E> c) { 
elementData = c.toArray(); 
size = elementData.length; 
// c.toArray might (incorrectly) not return Object[] (see 6260652) 
if (elementData.getClass() != Object[].class) 
  elementData = Arrays.copyOf(elementData, size, Object[].class); 
} 
 
public CopyOnWriteArrayList(Collection<? extends E> c) { 
Object[] elements = c.toArray(); 
// c.toArray might (incorrectly) not return Object[] (see 6260652) 
if (elements.getClass() != Object[].class) 
  elements = Arrays.copyOf(elements, elements.length, Object[].class); 
setArray(elements); 
} 

public static void test1() 
{ 
  SubClass[] subArray = {new SubClass(), new SubClass()}; 
  System.out.println(subArray.getClass()); 
 
  // class [Lcollection.SubClass; 
  BaseClass[] baseArray = subArray; 
  System.out.println(baseArray.getClass()); 
 
  // java.lang.ArrayStoreException 
  baseArray[0] = new BaseClass(); 
} 
 
public static void test2() 
{ 
  List<String> list = Arrays.asList("abc"); 
 
  // class java.util.Arrays$ArrayList 
  System.out.println(list.getClass()); 
 
  // class [Ljava.lang.String; 
  Object[] objArray = list.toArray(); 
  System.out.println(objArray.getClass()); 
 
  objArray[0] = new Object(); // cause ArrayStoreException 
} 
 
public static void test3() 
{ 
  List<String> dataList = new ArrayList<String>(); 
  dataList.add("one"); 
  dataList.add("two"); 
 
  Object[] listToArray = dataList.toArray(); 
 
  // class [Ljava.lang.Object;返回的是Object数组 
  System.out.println(listToArray.getClass()); 
  listToArray[0] = ""; 
  listToArray[0] = 123; 
  listToArray[0] = new Object(); 
   
}