does explicit upcasting save memory space?

[carpeliam]

i've got a subclass of something that carries a lot more information than the superclass. if i explicitly upcast an object of the subclass, will it still retain the information from the superclass? i'm looking to save memory.. and if i don't need everything from the superclass, i'd rather not return an object of superclass if i don't have to.

Liam Morley
lmorley@wpi.edu
"light the deep, and bring silence to the world.
light the world, and bring depth to the silence."

 

[idarke]

An object by itself hardly takes any memory. It's the objects that the class holds that take up space.

I did some experiments with JDevelopers "Memory Profiler", and I didn't see where casting affected the memory used except in those cases where I also used different constructors that did not create unnecessary class objects.

Try to avoid having objects initialized on a class level in the subclass:

Class Foo()
{
   Long x = new Long(1);

   public Foo()
   {
   }
}

Instead do this:

Class Foo()
{
   Long x = null;

   public Foo()
   {
      x = new Long(1);
   }
}

then arrange it so the subclass constructor does not get called.

As a side note, for a small program casting actually increases memory usage because of the additional ClassCastExceptions, etc that java brings in.

 

[hologram]

I don't think upcasting/downcasting changes anything of your object. (You can always cast it back, and you'll get all the info).

Maybe it is better to use composition instead of inheritence.