I'm confused about Polymorphism
- by Vtanathip
I'm know polymorphism rule that we can send it via parameter like this code
interface Animal {
void whoAmI();
}
class A implements Animal{
@Override
public void whoAmI() {
// TODO Auto-generated method stub
System.out.println("A");
}
}
class B implements Animal{
@Override
public void whoAmI() {
// TODO Auto-generated method stub
System.out.println("B");
}
}
class RuntimePolymorphismDemo {
public void WhoRU(List t){
System.out.println(t.getClass());
}
public static void main(String[] args) {
A a = new A();
B b = new B();
RuntimePolymorphismDemo rp = new RuntimePolymorphismDemo();
rp.WhoRU(a);
rp.WhoRU(b);
}
}
but
List<Example> examples = new ArrayList<Example>();
This code,I'm don't understand why we must use List.
why we can't use like this?
ArrayList<Example> examples = new ArrayList<Example>();
Because when we use List we can't use method that only have in ArrayList class like trimToSize()
and How I know when to use or not use?
