Dynamic Inheritance in Java

Question

Does such thing as dynamic inheritance exist in Java?

Just to clarify, by dynamic inheritance I mean: can I specify from what class I inherit certain class at runtime? (A inherits from { X | X ∈ {P, T, Q} })

I am just trying to understand what are my options if I need to implement, say, class Animal, which will have the following child classes: FlyingAnimal, WalkingAnimal, SwimmingAnimal, etc.

At the same time, I need to subdivide Animal into Humans and NonHumans, which will have slightly different behaviors. What I want to do is to derive Humans and NonHumans from Animal, and then derive Animal from Walkable, etc. - I want to decide which one it would be at the runtime (assuming that an animal can either walk, or fly).

Short answer: no. Long answer: noooooo. You cannot do this dynamically at runtime. — Louis Wasserman
– Louis Wasserman, Commented Apr 18, 2016 at 3:58
You should implement all the classes you need. And select one at the runtime. — user4910279
– user4910279, Commented Apr 18, 2016 at 4:03

Elliott Frisch · Accepted Answer · 2016-04-18 03:59:13Z

4

from what class I inherit certain class at runtime

No. Java is a compiled language with compile time type checking. However, it is possible to use a byte-code manipulation library like BCEL to create bytecodes at runtime; per the BCEL homepage one interesting application is the creation of classes from scratch at run-time

answered Apr 18, 2016 at 3:59

Elliott Frisch

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Pavlik Petrovich Over a year ago

Thanks @Elliot! I'll take a look at it, although, I don't feel that my Java knowledge is sufficient to get into byte manipulation (at least, yet). But is there a way to inherit class X from one class (A), and then do something like casting of the result to the instance of a child class (B)?

Has QUIT--Anony-Mousse · Accepted Answer · 2016-04-18 06:01:53Z

3

The proper way or solving such situations usually is (de-) composition and delegation (these are the keywords to search for).

For example, your class could contain an object of these classes, and simply use it instead of inheriting.

i.e.

interface Engine {}
class Diesel implements Engine {}
class Electric implements Engine {}
class Car /* NOT extends Diesel/Electric */ {
  Enigne engine; /* delegate or composition pattern */
}

answered Apr 18, 2016 at 6:01

Has QUIT--Anony-Mousse

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