Super Classes

[dapper sphinx]

This might just be a dumb question cus I recently started Java so please bare with me. But if i were to have multiple interfaces in one class what would the Super be?

[lost jungle]

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[raven garnet]

Superinterface is the description of an inheritance relation between two interfaces. If interface Car extends interface Vehicle, then the relation between Vehicle and Car is: "Vehicle is a superinterface of Car".

[dapper sphinx]

What if you have a normal clas with two interfaces

Or is that bad practice

[raven garnet]

Superinterfaces is between interfaces only. There is a second term, the Superclass. A normal class having two interfaces is very good practice.

[dapper sphinx]

Oh

Then if you were to call super in the class what would it call?

[raven garnet]

There are two kind of super. The constructor-super and the method-super.

What do you mean?

[dapper sphinx]

Can u explain both?

[raven garnet]

Sure, first the constructor super. Give me a secodn.

    public class Mercedes extends Car {
        public Mercedes(String designatedLicensePlate) {
            super(designatedLicensePlate);
        }
    }

    public class Car {
        private String licensePlate;

        public Car(String designatedLicensePlate) {
            this.licensePlate = designatedLicensePlate;
        }
        
        public String getLicensePlate() {
            return this.licensePlate;
        }
    }```

In line 3 you are reusing the constructor of the class Car.

Throu "super"

[dapper sphinx]

oh

so your doing

car(parameter); pretty much

but what would happen if you were to have

an extend

and an implement

and call super?

[raven garnet]

In line 1 you see the extend. In line 3 you see the super. The only thing left is the implement.

[dapper sphinx]

oh super(); is to get the constructor and super.method is to get the method of the super class in case of overrides and others?

[raven garnet]

Yes. But be aware of constructors without a parameter. They behave compleatly different!

[dapper sphinx]

oh

[raven garnet]

Constructors without arguments are called "default constructors". They do must not be called via "super", they call themselves automatically.

[dapper sphinx]

automatically?

how so

[raven garnet]

I dont know the reason. They just do it this way.

[dapper sphinx]

oh

if you were to do smth like this

how would you call jframe

or runnable

like

javax.swing.jframe?

[raven garnet]

First things first. The name "MyThread" is bad because the class is not a Thread. You better call it "MyRunnable" or "MyRunnableJFrame"

[dapper sphinx]

oh so if you make an object that has inherited classes and that inherited class is default that just runs

[dapper sphinx]

yeah thats true

i just chose a random name cus i was lazy

ik its bad practice tho

[raven garnet]

I would say "if you make an object that has inherited classes and that inherited class has default-constructor that just runs"

[dapper sphinx]

alr

thats makes sense

[raven garnet]

Your "MyRunnableJFrame" is aswell a JFrame AND a Runnable.

[dapper sphinx]

ye i just used it as an example of how would you call one or antoher

like how would u call the jframe

or the runnable

[raven garnet]

Just like the "Prince" is aswell a King-son AND a Queen-son.

[dapper sphinx]

ok

[raven garnet]

Ready for the super in methods?

[dapper sphinx]

sure

[raven garnet]

1 second

[dapper sphinx]

alr

[raven garnet]

        public void shout() {
            super.shout();
        }
    }
    public class Cat {
        public void shout() {
            System.out.println("Meow");
        }
    }

[dapper sphinx]

cat.shout?

[raven garnet]

idk

yes

[dapper sphinx]

oh

[raven garnet]

So in line 3 you see the super again but having a dot and then the reference to the Cat's shout-method.

[dapper sphinx]

yep

[raven garnet]

Not every cat sais "Meow". A lion is also a cat but a Lion should implement its very own version of "shout". "Roar" for example. So you will decide to not call the super.shout();

[dapper sphinx]

alr

[dapper sphinx]

oh ye for this if the super class were to have a parameter in the constructor how would you fix the error the unresolved compilation error

[raven garnet]

"Unresolved compilation error" can mean thousand things. Its like the "computer sais noooo".

[dapper sphinx]

when you extend this ig

how would you fix this from happening

or does it just normally not happen at all

[raven garnet]

"Something" have a constructor. Since there is the parameter "n" it is not the default-constructor.

[dapper sphinx]

true but is this just something that normally you shouldnt put a constructor into a parent class

[raven garnet]

Try to add public MyThreads() {super("");} to line 4 of "MyThreads"

[dapper sphinx]

oh it worked

how

[raven garnet]

MyThreads is a Something. And Something have no default-constructor. So the only way a Something can be constructed is by specifying the parameter "n". So the only way how "MyThreads" can be constructed is by specifying the parameter "n" aswell.

[dapper sphinx]

oh so this is a way of specifying the super class in the class

Classname() {super(some parameter)};

oh thats interesting

[dapper sphinx]

also one last question

i understand what you mean

but how would you call the king specifically

or the queen

if you just wanted one of the other

[dapper sphinx]

also is there a specific name for this

[raven garnet]

non-default-constructor-overwrite.

[dapper sphinx]

alright thank you

[lost jungle]

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[raven garnet]

You can not do that. You can neither ignore that the Lion is a Cat nor the Mercedes is a Car nor the MyThreads is a Something.

[dapper sphinx]

oh

but is there a way to

sorta just call ones method

like a king can have its own methods

[raven garnet]

You might be able to hide the concrete class using interfaces.

[dapper sphinx]

and a queen can have its own

and you can call upon a specific method from each

or is that not possible

[raven garnet]

You could hide methods using interfaces. But be aware that every instance extends from java.lang.Object. This is a thing you absolutly can not hide!

[dapper sphinx]

how would you call the methods in the interfaces

like lets say you overrode a method

and wanted the parents version of a method

but you have two interfaces

[raven garnet]

Give me a second

[dapper sphinx]

ok

[raven garnet]

        public void shout() {
            System.out.println("Meow");
        }
        public void purr(){
            System.out.println("Purrr");
        }
    }
    public interface Shoutable {
        void shout(); //"public" is added for all interfaces automatically by the compiler.
    }```

[dapper sphinx]

i mean in this case would super.shout(); not work?

[raven garnet]

No, super is a class thing, not an interface-thing.

[dapper sphinx]

oh

thats interesting

[raven garnet]

You could then create the cat using Shoutable tomcat = new Cat(); The type of the variable tomcat is "Shoutable".

Even if the Cat might have much more methods, you can not reference those methods throu the variable "tomcat" because "tomcat" is konw to be of type Shoutable only.

[dapper sphinx]

what

[raven garnet]

You can not write ```
Shoutable tomcat = new Cat();
tomcat.purr();

[dapper sphinx]

is cat an interface in this example

or smth

[dapper sphinx]

also what is a mycoon

[raven garnet]

I fixed the example, sorry for that

[dapper sphinx]

oh thanks

[lost jungle]

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[dapper sphinx]

why can't this be written tho?

[raven garnet]

You can google mycoon:

[dapper sphinx]

oh its a type of cat

[raven garnet]

Exactly

[dapper sphinx]

oh because the type is shoutable

you can only acces shoutable's methods

compared to

if you made the type Cat

[raven garnet]

Because the first Word in the Code is "Shoutable" and this defines what tomcat is allowed to be used.

[dapper sphinx]

oh

how come both of them would end with

new cat(); tho

does the end always reference the childclass?

and the beginning is what methods it can access

[raven garnet]

It should. It is good practice, it is called coding-against-interfaces (aka "program to interfaces, not implementations").

[dapper sphinx]

so coding against interfaces is how you access things within a class that implements an interface?

lik ehow you create an object

and how you access methods of its interfaces

[raven garnet]

Yes. You can reuse good-practice-code much better!

[dapper sphinx]

Oh ic

also is there any resource you recommend to use for someone who's tryna start java

[raven garnet]

Well, this is a question someone else should answer, this Posts are for concrete programming problems and questions only.

[dapper sphinx]

Oh alright

Well thank you for your time

[lost jungle]

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If you are not, please ignore this message.
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[dapper sphinx]

it was very informative

[raven garnet]

At your service!