Re: Novice to Generics Trying to Implement a Generic Priority Queue

Tom Anderson <>
Mon, 11 Apr 2011 22:41:05 +0100
On Mon, 11 Apr 2011, Daniele Futtorovic wrote:

On 11/04/2011 21:10, KevinSimonson allegedly wrote:

On Apr 11, 11:52 am, (Stefan Ram) wrote:

KevinSimonson<> writes:

Exception in thread "main" java.lang.ClassCastException:
[Ljava.lang.Object; cannot be cast to [Ljava.lang.Comparable;

( Da[] )new java.lang.Comparable[ size ]

Stefan, thanks! That solved the problem and my program works just
fine now.

This might be somewhat OK in this case, but it's hardly advisable.

A Comparable[] /is not a/ Da[].

You'd normally pass the Class object around in such cases:

 public PriorityQueue( Class<Da> component, int size )
   throws BadSizeException
   if (0<= size)
   { queue = (Da[]) Array.newInstance( component, size );

I'm not sure about 'normally'. That is certainly a known technique (for
those who haven't seen it, this use of a Class is called a 'type token'),
and whilst it may be advisable, i don't think it's more common than making
an array of some suitable static type and casting it uncheckedly [sic].
Does the JDK use it anywhere?


Taking care of business

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