Do companion objects remain in memory for app's lifecycle

Question

In Kotlin, you can create a singleton using a companion object:

class MyClass {
   companion object {
        fun doSomething() {

        }
    }
}

According to the Kotlin docs, it states:

Note that, even though the members of companion objects look like static members in other languages, at runtime those are still instance members of real objects...

https://kotlinlang.org/docs/reference/object-declarations.html

Does this mean that after using a function in the companion object, the instance of the class (MyClass) remains in memory for the entire lifecycle of the app? Is there a way in Android Studio to check to see if this is the case?

Answer 1

instance of the class (MyClass) remains in memory for the entire lifecycle of the app?

Companion object in JVM

in kotlin

class MyClass {
   companion object {
        fun doSomething() {

        }
    }
}

MyClass(Kotlin) converted in JVM

public final class MyClass {
   public static final MyClass.Companion Companion = new MyClass.Companion(null);

   public static final class Companion {
      public final void doSomething() {
      }

      private Companion() {
      }

      public Companion() {
         this();
      }
   }
}

As above code, companion object is declared as Companion class in JVM, and it's created as static field inside MyClass class. Thus, isn't collected by gc. So, the memory of object(Companion) is remained during the ProcessLifecycle. static final object isn't released in normal case.

In conclusion, if referred to MyClass.Companion instance in application, that instance will not be garbage collected. (on general Classloaders).

*If not referred to MyClass.Companion instance in application, it may be removed by code shrinking feature.

Is there a way in Android Studio to check to see if this is the case?

You can see through android studio > profiler > Heap dump.

Reference

• https://developer.android.com/topic/performance/memory-overview
• https://developer.android.com/studio/build/shrink-code