Java Array initialization with type casting

Question

The following code makes me confused:

Object[] arr1 = new String[]{"a", "b", "c"};
Object[] arr2 = {"a", "b", "c"};

String[] a = (String[]) arr1; // ok
String[] b = (String[]) arr2; // ClassCastException

System.out.println(arr1.getClass().getName()); // [Ljava.lang.String;
System.out.println(arr2.getClass().getName()); // [Ljava.lang.Object;

I am trying to understand why the two initialization are different from each other. The first one is a post declaration, while the second one is a shortcut. The two are both declared as Object[]

My naive understanding is that:

Object[] arr2 = {"a", "b", "c"}; // is a syntax sugar of
Object[] arr2 = new Object[] {"a", "b", "c"};

So the runtime type of arr2 is exactly Object[] which can not be converted into String[].

But the things get strange here, because Java Array is covariant: String[] is a subclass of Object[] and arr2 is exactly a String[], casting back from Object[] to String[] on arr2 should work.

Any explanation on this is high appreciated.

Answer 1

Because arr2 is an Object[], there's nothing stopping you from writing

arr2[0] = new Object();

right before your cast, case in which the cast would no longer make sense anyway.

Because of the way initializer syntax works, also note the following:

Object x = {"a", "b"}; // error: illegal initializer for Object
Object[] a = {"a", "b"}; //a has class [Ljava.lang.Object; 
String[] b = {"a", "b"};  //b has class [Ljava.lang.String; 

The compiler determines whether you want your array to be an Object[] or a String[] based on your declaration.