#Interface Inheritance

1 messages · Page 1 of 1 (latest)

weary radish
#

Why can't I call previous implementations of the show() method in this example?

public interface TopLevel {
    default void show() {
        System.out.println("Top level");
    }
}

public interface MidLevel extends TopLevel {
    @Override
    default void show() {
        System.out.println("Mid Level");
    }
}

public interface LowLevel extends MidLevel {
    @Override
    default void show() {
        System.out.println("Low Level");
    }
}

public class Lmao implements LowLevel{
    @Override
    public void show() {
        System.out.println("Lmao");
        LowLevel.super.show();
        MidLevel.super.show(); //Error
    }
}
sacred sedgeBOT
#

<@&987246399047479336> please have a look, thanks.

remote sundial
#

Well, if you call super.show(), you will call LowLevel.show(). But LowLever overrides the MidLever show.

#

Your class lmao overrides the LowLevel show()

weary radish
#

Yeah, but why I can call LowLevel.super.show() but can't MidLevel or TopLevel

sour goblet
#

LowLevel.... in this context is identical to not writing it at all

#

so what u wrote is just super.show()

#

u can't put the class name there to access a specific version of the method, that's not a thing

#

the only reason u could write LowLevel there is bc ur current class is LowLevel

#

its more or less just ignored

#

the class name in front makes sense for static methods

#

but u dont have a static method here

peak urchin
#

in my computer, default void show() { isnt useble at all. how could it be

#

?

weary radish
peak urchin
#

but what does the code have to do in general?

weary radish
#

It's just test of InterfaceName.super.defaultMethod() construction in general

sour goblet
#

what u wrote makes, java-wise, no sense. and hence doesnt work

#

and LowLevel.super.show() is simply identical to just writing super.show()

peak urchin
weary radish
#

I tried to use InterfaceName.super.defaultMethod() construction with inheritance and I was stumped

#

Book is java - the complete reference book Herbert Schildt

#

If I write MidLevel.super.show() in the LowLevel interface instead of in the Lmao class it works, but I don't understand why

peak urchin
#

im a bit new to java, but if im not wromg, ur book may be up to date

#

from what year is it?

weary radish
#

This edition about java 17 version

#

I'm using java 21

#

But I don't think it should create conflict

#

Backward compatibility is one of the main principles of java, after all

peak urchin
weary radish
#

I have an idea that in this way you can call an implementation only 1 level higher in the inheritance chain, but I haven't found any confirmation of this, so I can't be 100% sure about it

#

Because

public interface LowLevel extends MidLevel {
    @Override
    default void show() {
        //MidLevel.super.show();      NO ERROR
        System.out.println("Low Level");
    }
}
``` gonna work
sour goblet
# weary radish

whats written in that book is correct but ur code doesnt represent that situation

sacred sedgeBOT
sour goblet
#

u cant refer to ur grandfather, as that is the business of ur direct father to deal with

#

thats how inheritance works

weary radish
sour goblet
#

yes. u can either say "my stuff or the stuff of my father"

#

u cant say "or my grandfathers"

weary radish
#

Oh, thank you very much

sour goblet
#

what the book shows is sth different. its for when u have two direct parents

#

i.e. the diamond problem

weary radish
#

I understand it now

peak urchin
#

oh now its clear.thnx

sacred sedgeBOT
#

@weary radish

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