Java - Why declare an array as a type of Interface? -

this professor mark weiss in book data structures , algorithm analysis in java

public class binaryheap<anytype extends comparable<? super anytype>>{     private void enlargearray( int newsize ){         anytype [] old = array;         array = (anytype []) new comparable[ newsize ];         for( int = 0; < old.length; i++ )         array[ ] = old[ ];             } } 

i wondering why declare array type of interface comparable since have convert comparable[] anytype[]? design philosophy in there?

the design "philosophy" can't instantiate array of type parameter, have instantiate array type legal. available legal types known method array of object or of comparable, , latter captures more knowledge type.

you allowed downcast array of type parameter, , return type has that, downcasting required.

it's "philosophy" of necessity.