Accessing Kotlin extension functions from Java

Question

Is it possible to access extension functions from Java code?

I defined the extension function in a Kotlin file.

package com.test.extensions

import c         


        

Answer 1

Kotlin top-level extension function are compiled as Java static methods.

Given Kotlin file Extensions.kt in package foo.bar containing:

fun String.bar(): Int {
    ...
}

The equivalent Java code would be:

package foo.bar;

class ExtensionsKt {
    public static int bar(String receiver) { 
        ...
    }
}

Unless, that is, Extensions.kt contained the line

@file:JvmName("DemoUtils")

In which case the Java static class would be named DemoUtils

In Kotlin, extension methods can be declared in other ways. (For example, as a member function or as an extension of a companion object.)