Object[] class name?

i just confuse about how arrays work.

int[] (or other primitive array) somehow is subclass of java.lang.Object

so does Object[].

so both are Object.

here, its a anomaly :

Object o = new Something();

if (o instanceof Object) System.out.println("okay");

o = new int[0];

if (o instanceof Object) System.out.println("okay");

int[] aPrimitiveArray = new int[0];

if (aPrimitiveArray instanceof Object) // will compile error

j_shadinataa at 2007-7-12 17:20:14 >

class Test {

public static void main(String[] args){

Object o = new Object();

if(o instanceof Object)

System.out.println("ok");

o = new int[10];

if(o instanceof Object)

System.out.println("ok");

int[] k = new int[10];

if(k instanceof Object)

System.out.println("ok");

}

}

prints 3 ok's for me.

prob.not.sola at 2007-7-12 17:20:14 >

> Yeh, the compiler is smart enough to know that a primitive array is not ever going to be an instance of a reference array, and tells you so. Because it isn't

i see... & the fact its not just array.

since it's definitely return false, so compiler reduce our time compiling it :P

j_shadinataa at 2007-7-21 21:45:42 >

> from where [I come ?

It's name of the class of an array of ints. The [ implies you have an array and the I tells you that the component type is int. The syntax is specified in section 4.3.2 of the VM spec.

http://java.sun.com/docs/books/jvms/second_edition/html/ClassFile.doc.html#14152

jsalonena at 2007-7-21 21:45:42 >

> That's because there is no class construct for an

> array. The runtime generates it for you as needed.

> Arrays are a monumental pain in the @rse if you're

> dealing with them reflectively, for this reason :-(

> blo0dy java

What are you talking about? Arrays have well defined classes just like all other objects in Java. The class name just happens to not be a valid Java identifier so you can't use the usual syntax to instantiate, but this is no problem to reflection. For example you can writeClass cls = Class.forName("[[D"); // array of arrays of doubles

Well, the class doesn't have any constuctors, fields, or methods, so it's not very useful...

jsalonena at 2007-7-21 21:45:42 >

> > That's because there is no class construct for an

> > array. The runtime generates it for you as needed.

> > Arrays are a monumental pain in the @rse if you're

> > dealing with them reflectively, for this reason

> :-(

> > blo0dy java

>

> What are you talking about? Arrays have well defined

> classes just like all other objects in Java. The

> class name just happens to not be a valid Java

> identifier so you can't use the usual syntax to

> instantiate, but this is no problem to reflection.

> For example you can writeClass cls =

> Class.forName("[[D"); // array of arrays of

> doubles

Well, the class doesn't have any

> constuctors, fields, or methods, so it's not very

> useful...

What I mean is, arrays have to be dealt with specifically when you're reflecting upon them, you often can't just pass them through the same old reflective code as any other object

georgemca at 2007-7-21 21:45:42 >

> But apparently you can't access them through the class instance.. when you list the

> fields the array comes out empty.

It it occured to me I didn't know whether by "the class" you meant the class associated with the array (which does have .length) or the Class cls (which doesn't make .length or clone() available).

pbrockway2a at 2007-7-21 21:45:42 >

well your line 3 should never work, so that behaviour is correct.

and it's true that the 'superclass' (as returned by getSuperclass()) for all arrays is object, but it means little because they are also subclasses of their parents arrays, like so:

public class Test {

public static void main(String[] args){

Object[] obj = new C[10];

System.out.println(obj.getClass().getSuperclass().getName());

System.out.println(obj instanceof B[]);

}

}

class A { }

class B extends A { }

class C extends B { }

which, honestly, i like.

prob.not.sola at 2007-7-21 21:45:49 >