Is it possible to override static method in Kotlin?

Question

Hello imagine that we have following class

Manager{
   public static void doSth(){
      // some logic
   };
}

How to override that method in kotlin?

I've tired to use

fun Manager.doSth(){}

but Its applied to instance not a static type.

Purpose of doing that is to avoid using PowerMockito

What you call "override" would actually mean "replace", i.e., monkey-patch the original declaring class. You can't override non-virtual methods. — Marko Topolnik, Jul 10 '18 at 13:17
Polymorphism and the static keyword are conflicting concepts. What you are suggesting is not possible because it does not make sense. I suggest you read up on [what static really means](https://stackoverflow.com/questions/413898/what-does-the-static-keyword-do-in-a-class) — Michael, Jul 10 '18 at 13:21
@Pawel Shadowing is much lighter-weight, it just affects the resolution of unqualified names. This is not what OP is after. — Marko Topolnik, Jul 10 '18 at 13:26
I didn't know monkey-patch before, but I will read about it. Don't understand why sb downvoted it? Does this question break stackoverflow rules? If not, why you did it? — murt, Jul 10 '18 at 13:46
@MarkoTopolnik does "monkey-patch" is the only solution for that? Do you know if PowerMockito use it to replace static methods? — murt, Jul 10 '18 at 13:47
I can only suppose what it does: jack into the class loading mechanism and replace the bytecode of a static method. — Marko Topolnik, Jul 10 '18 at 13:59

Ahmed Hegazy · Accepted Answer · 2019-06-24T08:22:38.943

Short Answer

No

"Short" Explanation

You can only override virtual methods and also you can shadow/replace static methods in Java, but you can't shadow a "static" method in Kotlin as the static method will not be available using the child class qualifier already. And even when using extension methods, you simply can't do it for either static or non-static as the member function will always win(see the example below). What you can do is to subclass the parent and add a new companion object that has a method with the same name as the parent and call the parent method from inside.

Full Explanation

Static methods can't be overridden. It's called shadowing as you hide a method with another one.
There are no static methods in Kotlin, so what you can do is using the companion object which behaves similarly and you can access the method of the companion object as if it were a java static method using only the class name as a qualifier but you can't access the methods of companion object of a parent class from its child like Java.
You can't shadow a static method in Kotlin as the static method will not be available using the child class qualifier already, but you can write another companion object and add a method with the same name and call the parent method from there as the method from parent can't be accessed with the child class name qualifier.
You can't make an extension method that shadows a companion object method or even overrides a member method. If a class has a member function and an extension function is defined which has the same receiver type, the same name and is applicable to given arguments, the member always wins.
Companion object extension: You can write an extension method to the companion object, but if a member of that companion object has the same signature the member will always win.

Example

open class A {
    fun foo() {
        println("A.foo()")
    }
    companion object {
        fun bar() {
            println("A.Companion.bar()")
        }
    }
}

class B: A()

fun A.foo() {
   println("A.foo() extension")
}

fun A.Companion.bar() {
    println("A.Companion.bar() extension")
}

fun A.Companion.baz() {
    println("A.Companion.baz() extension")
}

fun main(args: Array<String>) {
    A().foo() // prints A.foo()
    A.bar() // prints A.Companion.bar()
    A.baz() // prints A.Companion.baz() extension
    B.bar() // COMPILE ERROR
}

Yeah, the thing is that the static method from the parent can't be accessed from the child's qualifier so it can't be shadowed. Using extensions, you simply can't do it for either static or non-static as the member function will always win. What you can do is to subclass the parent and add a new companion object that has a method with the same name as the parent. — Ahmed Hegazy, Jul 11 '18 at 12:36

score 2 · Answer 2 · answered Jul 10 '18 at 15:23

You can't do that in Kotlin. The problem is that there is no static keyword in Kotlin. There is a similar concept (companion object) but the problem is that your original Java class doesn't have one.

static methods don't support inheritance either so you can't help this on the Java side.

If you want to declare extension methods which are "static" (eg: put them on a companion object) you can do this:

class Manager {

    companion object
}

fun Manager.Companion.doSth() = println("sth")

Then you can call it like this:

Manager.doSth()

Note that you can only augment Kotlin classes this way which have a companion object.

Is it possible to override static method in Kotlin?

2 Answers2

Example

Linked