Java static methods vs overriding

Question

Trying to work on an example from a book on method overriding. The code has two classes Veggies and Pumpkin.The only confusion i have is if the object of pumpkin is assigned to the myveggie object, why does it call the method of veggies class since the object is from derived class. I am sure this has something to do with static method,but I could get a more clear idea.

 class Veggies {
        public static void staticMethod(){
            System.out.println("Veggies static method");
        }
    public void instancemethod(){
        System.out.println("Veggies instance method");
    }
}
public class Pumpkin extends Veggies{
        public static void staticMethod(){
            System.out.println("Pumpkin static method");
        }
        @Override
        public void instancemethod(){
            System.out.println("Pumpkin instance method");
        }
        public static void main(String[] args) {
            Pumpkin myPumpkin=new Pumpkin();
            Veggies myveggie=myPumpkin;
            myveggie.staticMethod();
            myveggie.instancemethod();

        }
    }

Any sane IDE will warn you that you call a static method as instance method. — Johannes Kuhn, Mar 07 '18 at 14:26
Static methods are methods that are relative to a class, not to an instance. In my opinion, you should never call static methods on an instance (i.e. I would replace `myveggie.staticMethod()` with `Veggies.staticMethod()`), it is confusing — Oneiros, Mar 07 '18 at 14:28
i think that there is a problem with the inner class, if you seperate them in two different classes it will work fine — Elarbi Mohamed Aymen, Mar 07 '18 at 14:30

Stephen C · Accepted Answer · 2018-03-07T15:53:03.510

2

As this question:

Why doesn't Java allow overriding of static methods?

explains, static methods cannot be overridden in Java.

What you have in your example, is code that is calling a static method via an instance. This is bad practice.

What actually happens is that the static type of the variable (not the reference!) is resolved at compile time to a class. In this case, the class is Veggies. Then the compiler inserts a call to the static method of that class; i.e. Veggies.staticMethod().

Which is confusing ... because it looks like you should be dispatching to a static method associated with the reference. But that is not how Java works.

That's why this is bad practice, and why a lot of IDEs will warn you about it.

edited Mar 07 '18 at 15:53

answered Mar 07 '18 at 14:35

Stephen C

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So despite the object referrence, it still basically resolves to Veggies.staticMethod()? – Bissi singh Mar 07 '18 at 14:42
1

@Bissisingh That's it, if you call a static method what decide which method is called is defined by the type of the variable not the type of the object referred by. – Jean-Baptiste Yunès Mar 07 '18 at 14:47

Java static methods vs overriding

1 Answers1