Singleton class in Kotlin

Question

I want to know way to create singleton class, so that my Util class instantiate only once per app. However when I converted my Java class to kotlin, below code was generated

Answer 1

There is a special keyword object for singletons in Kotlin. You can just type something as simple as this to get working singleton class:

object MySingleton

or when you want some member functions:

object MySingleton {
    fun someFunction(...) {...}
}

And then use it:

MySingleton.someFunction(...)

there is a reference: https://kotlinlang.org/docs/reference/object-declarations.html#object-declarations

EDIT:

In your case, you just need to replace in your definition of class UtilProject to this:

object UtilProject {

    // here you put all member functions, values and variables
    // that you need in your singleton Util class, for example:

    val maxValue: Int = 100

    fun compareInts(a: Int, b: Int): Int {...}
}

And then you can simply use your singleton in other places:

UtilProject.compareInts(1, 2)
//or
var value = UtilProject.maxValue