What re the restrictions around Java EXPLICIT type conversion?

Question

public class TypeConversion {
    Human human = new Human();
    NonHuman nonHuman = new NonHuman();
    
    public void test()
    {
        nonHuman = (NonHuman) human; //Cannot cast from Human to NonHuman
    }
}

class Human { }
class NonHuman {}

I was expecting the type conversion to work as its explicit, atleast at compile-time. And result in to a ClassCastException or some thing similar at run-time.

So, I am interested to know what are the restrictions around type conversion at compile time.

Something that is stored in a `Human` can NEVER be a `NonHuman`, the compiler can know that. — luk2302, Dec 04 '20 at 09:30

Ragesh G R · Answer 1 · 2020-12-04T09:34:31.260

1

Random classes cannot be typecastes/converted to each other.

Two types of conversions are usually allowed Conversion of a sub class object into a superclass variable (Implicitely) Conversion of a superclass object into a sub-class variable (Explicitely)

So your case would work only if the two classes had a parent child or a child parent relationship.

edited Dec 04 '20 at 09:34

answered Dec 04 '20 at 09:33

Ragesh G R

39
8

1

You can always cast to an interface type as well, even if it "seems" unrelated to the class. – Joachim Sauer Dec 04 '20 at 09:33
yes but that would be different from what the OP is trying to achieve – Ragesh G R Dec 04 '20 at 09:35
1

@JoachimSauer, that's wonderfull to add. Thanks both. +1 – samshers Dec 04 '20 at 09:46
@samshers you are not getting bashed, one downvote is not much - if you were to accept this answer you should have a net gain/loss of 0 reputation afaik. – luk2302 Dec 04 '20 at 11:34
I don't see any bashing – Ragesh G R Dec 04 '20 at 11:57

What re the restrictions around Java EXPLICIT type conversion?

1 Answers1