Behaviour of final static method

user_211599 0
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I have been playing around with modifiers with static method and came across a weird behaviour.

As we know, static methods cannot be overridden, as they are associated with class rather than instance.

So if I have the below snippet, it compiles fine

//Snippet 1 - Compiles fine
public class A {
    static void ts() {
    }
}

class B extends A {
    static void ts() {
    }
}

But if I include final modifier to static method in class A, then compilation fails ts() in B cannot override ts() in A; overridden method is static final.

Why is this happening when static method cannot be overridden at all?

methods final static java
8 Answers

A static method can't be overridden in Java, unlike non-static methods. But they are inherited like static and non-static data members. That is why a non-static method with the same name can't be created in the parent class

class Writer { 
    public static void doo(){
        System.out.println("sth");
    } 
}
class Author extends Writer{ 
    public void doo(){
        System.out.println("ok"); // error overridden method is static
    }
}

The final keyword ensures that the specific method body be run everytime a call to the method. Now if a static method is created in the child class with the same name and a call to the method is made, the method in the subclass gets executed which should not be the case if final is prefixed before the static method name in the parent class. Hence final keyword restricts the creation of method with the same name in the child class.

user_89534250

Static methods are "hidden" in inherited classes and cannot be overridden "non-statically" i.e. they cannot be overridden in a "polymorphism" sense. But they can be overridden "statically".

Static final methods are not allowed to be overridden even "statically".

The following example illustrates this -

App.java -

public class App {
    public static void main(String[] args) {
        Base.fun1();
        Base.fun2();
        Derived1.fun1();
        Derived1.fun2();
        Derived2.fun1();
        Derived2.fun2();
    }
}

Base.java -

public abstract class Base {

    protected static void fun1() {
        System.out.println("Static fun1() called in Base");
    }

    protected static final void fun2() {
        System.out.println("Static final fun2() called in Base");
    }

}

Derived1.java -

public class Derived1 extends Base {

    protected static void fun1() {
        System.out.println("Static fun1() called in Derived1");
    }
    
    //Not allowed to override final method
    /*
    protected static final void fun2() {
        System.out.println("Static final fun2() called in Derived1");
    }
    */
}

Derived2.java -

public class Derived2 extends Base {

    protected static void fun1() {
        System.out.println("Static fun1() called in Derived2");
    }
    
    //Not allowed to override final method
    /*
    protected static final void fun2() {
        System.out.println("Static final fun2() called in Derived2");
    }
    */
}

Output -

Static fun1() called in Base
Static final fun2() called in Base
Static fun1() called in Derived1
Static final fun2() called in Base
Static fun1() called in Derived2
Static final fun2() called in Base
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