Can't cast ....

[Prashant Neginahal]

Hi All,
You can't cast any primitive array to another primitive array type even with explicit cast. But is possible for arrays of Object references.

[Anonymous]

No, you can't cast that either. Have a look at the following example:
abstract class Vehicle { ... }
public class Car extends Vehicle { ... }
public class Submarine extends Vehicle { ... }
Vehicle[] v= new Vehicle[42];
Car[] carPark= (Car[])v; // suppose this works
v[0]= new Submarine(); // you've got a submarine in your carpark now ...
kind regards

[Bert Bates]

Prashant -
But for polymorphic purposes you can do the following:

class Animal { }
class Cat extends Animal{ }
public class TestCat {
  public static void main(String [ ] args) {
     Animal [ ] aa = new Animal[4];
     Cat [ ] ca = (Cat[ ] ) aa;   // casting an array
     //   or
     Animal [ ] aa2 = new Cat[ 3 ];
  }
}

So just as you might want to make polymorhic calls on objects, you can make polymorphic calls on arrays of objects.
[ December 27, 2002: Message edited by: Bert Bates ]

[Ilja Preuss]

But you can do the following:

Vehicle[] v= new Car[42];
Car[] carPark= (Car[])v; // this works
v[0]= new Submarine(); // you get a runtime exception here

[Ilja Preuss]

Originally posted by Bert Bates:

class Animal { }
class Cat extends Animal{ }
public class TestCat {
  public static void main(String [ ] args) {
     Animal [ ] aa = new Animal[4];
     Cat [ ] ca = (Cat[ ] ) aa;   // casting an array

Did you try this? AFAIK this should give you a runtime exception...

[Bert Bates]

OOOOPS !!!
Sorry - but the line :
Animal [ ] aa2 = new Cat[3];
is ok.... :roll:
(jeez - some days I just shouldn't even get out of bed - and I should never post before that first cup of coffee

[Anonymous]

Originally posted by Ilja Preuss:
But you can do the following:

Vehicle[] v= new Car[42];
Car[] carPark= (Car[])v; // this works
v[0]= new Submarine(); // you get a runtime exception here

Yes, but that's a bit besides the point because during runtime the RTTI of variable v clearly shows that v already *is* a Car[], so no cast, neither upwards or downwards needs to be applied. My example showed that downcasting arrays (if allowed) would be an infringement of the type safety which is supposed to be guaranteed, hence it is not allowed.
kind regards

[Ilja Preuss]

Originally posted by Jos Horsmeier:

Vehicle[] v= new Car[42];
Car[] carPark= (Car[])v; // this works
v[0]= new Submarine(); // you get a runtime exception here

<hr></blockquote>
Yes, but that's a bit besides the point because during runtime the RTTI of variable v clearly shows that v already *is* a Car[], so no cast, neither upwards or downwards needs to be applied.[/QB]

But that's true for casting *any* object (in contrast to casting primitive types). In fact, casting always only affects the reference, never the object itself.