i have 2 questions what is difference between .toString and as String second question is: can we do ...

# getting-started

[Muhammet Emin Gündoğar]

i have 2 questions what is difference between .toString and as String second question is: can we do both upcasting and downcasting with as keyword?

[Ruckus]

.toString() is a conversion, whereas as String is a cast (it doesn't convert, it falls if the receiver is not a String).

[Ruckus]

You can cast however you want with as, but that doesn't mean the cast will always succeed.

[Muhammet Emin Gündoğar]

@Ruckus There is an error in android studio this cast never succeed.If we try unrelated cast.

[Muhammet Emin Gündoğar]

i am asking which casts can succed always

[Muhammet Emin Gündoğar]

up to down and down to up can work always?

[Ruckus]

I think you are misunderstanding what casting is. Casting doesn't change the receiver, it just tells the compiler "hey, you may not know it, but this thing is definitely a [whatever you're casting to], so treat it as such."

The error is the compiler telling you "I see what you're saying, but I can guarantee there is no possible way this thing is really a [whatever you're casting to], so this cat will always fall."

[Ruckus]

Casting to a super type will always work, but casting to a sub type will only work if it is that type.

[Muhammet Emin Gündoğar]

can we cast from "any" class to everything

[Ruckus]

You can, but that doesn't mean the cast will succeed.

[Ruckus]

val x: Any = 5
x as String  // falls, x is an Int, not a String

[Muhammet Emin Gündoğar]

ok.I see it is so clear now.Thank you

[Muhammet Emin Gündoğar]

Lastly is casting more efficient than conversion? ı heard that but i wanted to be sure

[Ruckus]

They're two different things with different purposes. It doesn't make sense to ask which is more efficient. Which one you use depends on what you're trying to do.

[Muhammet Emin Gündoğar]

ok.thanks