Java override

[empty marsh]

i get "Method does not override method from its superclass"

public class MallardDuck extends duck{
    @Override
    public static void display(){
        System.out.println("A mallard duck appears");
     }

}

[signal sleet]

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

[empty marsh]

base class

package com.company;

public class duck {
    public static void quack(){

    }

    public static void swim(){

    }

    public static void display(){
        System.out.println("A duck appears");
    }
}

what am i doing wrong?

[hallow quail]

Static methods in java are not (and cannot be) 'virtual'. They aren't inherited from a parent and cannot be overridden.

Unfortunately Java has two places (that continue to exist for backwards-compatibility) that make this confusing. And child static method can therefore 'shadow' a parent static method.

Calling a static method using a subclass makes it look like the method is inherited. And calling a static method from a reference makes it look like it should use inheritance too

class Parent {
   static void m() { System.out.println("Parent"); }
}

class ChildWithoutM extends Parent {}
class ChildWithM extends Parent {
   static void m() { System.out.println("Child2"); } // 'shadows' the Parent m()
}

...

ChildWithoutM.m(); // this is actually compiled as Parent.m() and prints "Parent"
ChildWithM.m(); // this prints "Child2"

Parent o = new ChildWithM();
o.m(); // this is actually compiled as Parent.m() and prints "Parent". It uses the declaration type of o.

It is popular, using build-tools and/or continuous-integration, to enforce that static methods are called only via class literals, and only from the declaring class so that this confusing usage is not allowed.,

There are languages in which virtual class methods exist - but it's rare, and requires that you can declare variables of class types and class-families. Java doesn't have these concepts (and they're only occasionally useful).

[empty marsh]

oh , but i still dont understand why the last statement calls parent.m() ?
o is assigned to childWithM? and that has a method which shadows parent.m() ?

so the output should be child2?

[hallow quail]

No. That's the illusion this unfortunate grammar feature implies. But static methods are not inherited. The type of the reference o is Parent and so Parent.m() is what compiler resolves.

[empty marsh]

oh , i see , thank you

also , do i have to put the class files inside the com.company "package?" folder?

or i can put then directly in src folder?

[swift niche]

you can put them directly if you want

all classes live inside a package

so MallardDuck is in the com.company package

and you probably see a package com.company; at the top

if you put it right under src and remove that line it is in "the unnamed package"

which works, but small caveat - code in named packages can't import from the unnamed package