Builder
Excuse the simplicity of this question.
I want to employ generics for a Factory.
For example, suppose I have an Animal interface, and then the usual animal implementations: a Dog, a Cat etc.
Creating my animal objects is quite complex (involves database calls etc) so I have decided to have a Builder class which has a number of static builder methods for making them.
For example:
publicstatic Dog createDog()
publicstatic Cat createCat() etc.
The creation code is quite similar for all the animals it's the return type that is key different part.
I could of course have a
publicstatic Animal createAnimal(class animalType)
but then I would have loads of ugly casting in my code, So I thought generics could help me out here,
I tried something like:
publicstatic <T> Animal <T> createEntity(T type)
however the Animal interface is not a generic.
Ok, I am confused as how do something I thought would be simple?
Should I make the Animal interface a generic or if not can I use any of the generica interfaces to help me out.
[1436 byte] By [
beginner2a] at [2007-11-26 23:59:04]
# 1
You mean something like this?
class Main {
public static void main(String[] args)
throws InstantiationException, IllegalAccessException {
Cat cat = AnimalFarm.getAnimal(Cat.class);
Dog dog = AnimalFarm.getAnimal(Dog.class);
System.out.println("cats say: "+cat.makeSound());
System.out.println("dogs say: "+dog.makeSound());
}
}
class AnimalFarm {
static <T> T getAnimal(Class<T> type)
throws InstantiationException, IllegalAccessException {
Object obj = type.newInstance();
return type.cast(obj);
}
}
interface Animal {
public String makeSound();
}
class Dog implements Animal {
public String makeSound() { return "Wooff!"; }
}
class Cat implements Animal {
public String makeSound() { return "Meoww!"; }
}
# 4
May I suggest a minor tweak:
class AnimalFarm {
static <T extends Animal> T getAnimal(Class<T> type) throws InstantiationException, IllegalAccessException {
return type.newInstance();
}
}
This ensures that you only construct animals with the getAnimal method.
# 5
> Yeah that works, I am interesting that you still have
> to call the .cast().
Good call! As raindrop already posted: you don't have to.
Also note the change PeterAhe proposed: he is right, you should restrict T to be of type Animal.
> Thanks for your time.
You're welcome.
; )
