Kotlin companion object vs global function

Kotlin The companion of （companion object） Grammatically similar to Java Static methods in , So many people use it like this . This article will show you how companion objects work and in Kotlin Recommended Practice for creating static methods in .

Companion Companion Objects

Is a class declared inside with companion Keyword marked objects . Grammatically, it is similar to Java Static methods in ： You can call the members in the object through the class name .

The code is generally like this ：

//  Statement 
class KCompanion {
    companion object{
        fun getBongs(nTimes: Int) {
            for (i in 1 .. nTimes) {
                print("BONG ")
            }
        }
    }
}
//  call 
KCompanion.getBongs()

It's pretty simple, isn't it ！ Even if the members of the companion object look like static members in other languages , At runtime, they are still member instances of real objects .

Let's see what happens after the code is compiled ：

public final class KCompanion {
     ... 
  public static final class Companion {
      public final void getBongs(int nTimes) {
         ...
      }
   }
}

An extra  Companion  class It's created . How to avoid creating this class ？ We can use global functions to realize our requirements .

Global function

Create a kotlin file Bong.kt, Then write the methods we want to be accessible everywhere as static projects ：

fun getBongs(nTimes: Int) {
    for (i in 1 .. nTimes) {
        print("BONG ")
    }
}
fun someOtherMethod() {
      print("BONG ")
   
}

In this way, you can directly access the package visible functions , No qualifiers are required ：

//  Call global functions  
 getBongs(5)

Let's see what the compiled code looks like ：

public final class BongKt {
   public static final void getBongs(int nTimes) {
        ...
   }
   public static final void someOtherMethod() {
        ...
   }
}

You can see , The compiled code does not create additional classes .

summary ： If you can , When you want to use companion objects companion object when , Consider using global functions instead ~