instance of

[srinivas sridaragaddi]

interface face{}
class bar implements face{}
class foo extends bar{}

foo[] instanceof foo,bar,face is false
foo[1] instanceof foo,bar,face,Object is true

K&B book page no 286
can any one explain what is happening here...

[suresh mulagala]

i guess foo[1] is initialized and an instance but foo[] may not be one...

[Burkhard Hassel]

Howdy cowboys,

there is an erratum on that page.
An instance of and array of any type is not an instance of that type, only an instance of an array of that type.
- Ehem. To explain:

interface Face { }
class Bar implements Face{ }
class Foo extends Bar { }
 
class Main {
public static void main(String[] args) {
Foo[] fooarray = { new Foo() };
// System.out.println(fooarray instanceof Foo);
System.out.println(fooarray instanceof Foo[]);
System.out.println(fooarray instanceof Bar[]);
System.out.println(fooarray instanceof Face[]);
}
}

Due to the table, the outcommented line would print "false" if commented in.
But it would not print "false", it would not compile.
Because a Foo[] is an Array, it is not in the hierarchy line of Foo, so it cannot compile.


So the fifth line of the table:

Foo [ ]         Foo, Bar, Face           false
 
    should be
Foo []          Foo, Bar, Face           does not compile.

This is not yet listed on the errata page.


Thanks,
Bu.

[srinivas sridaragaddi]

Hi Burkhard,


Thanks for letting us know about the errata...

i was about to mess up every thing as it was not found on errata..
thank you