Hands-On Design Patterns with Kotlin

Static Factory Method in Kotlin

We've already discussed the object keyword earlier in the Singleton section. Now we'll see another use of it is a companion object.

In Java, Static Factory Methods are declared static. But in Kotlin, there's no such keyword. Instead, methods that don't belong to an instance of a class can be declared inside a companion object:

class NumberMaster {    companion object {        fun valueOf(hopefullyNumber: String) : Long {            return hopefullyNumber.toLong()        }    }}

Companion objects may have a name: companion object Parser, for example. But this is only for clarity of what the goal of this object is.

Calling a companion object doesn't require instantiating a class:

println(NumberMaster.valueOf("123")) // Prints 123

Moreover, ...