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From: mg@dsd.camb.inmet.com (Mitch Gart)
Subject: Re: Java vs Ada 95 (Was Re: Once again,
 Ada absent from DoD SBIR solicitation)
Date: 1996/10/15
Message-ID: <DzBM79.52n.0.-s@inmet.camb.inmet.com>#1/1
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references: <ROGOFF.96Oct14095012@sccm.Stanford.EDU>
organization: Intermetrics, Inc.
newsgroups: comp.lang.ada
Date: 1996-10-15T00:00:00+00:00
List-Id: <comp.lang.ada>


Brian Rogoff (rogoff@sccm.Stanford.EDU) wrote:
: Besides GC, which is arguable, no one has 
: listed any *language* advantages of Java over Ada. 

Calling superclass methods is easy in Java and hard in Ada:

  type parent_obj is tagged record ...;
  type parent_ptr is access all parent_obj;
  procedure p(param: access parent_obj);

  type child_obj is new parent_obj with ...;
  type child_ptr is access all child_obj;
  procedure p(param: access child_obj);

now inside the child's p, to call the parent's p:

  p(parent_obj(param.all)'access);

is the way to do it.  Converting the pointer to parent_ptr won't work because
the call will dispatch back to the child.  This ".all'access" trick is pretty
painful.  In Java the keyword "super" does what's wanted:

  super.p();

Calling the parent type's operation is common in OOP and is painful to code, 
and read, in Ada.

- Mitch