Android Call Kotlin Object from Java

Call Kotlin from Java

These days, developing Android app by kotlin becomes popular. But, sometimes we need to support Java App, continues from the past.
I developed Kotlin base mobile SDK, and some customers need to use this SDK from Java

Kotlin Object and Companion Object

When creating SDK in kotlin, there are 2 types of Java static like method in kotlin

Object and Companion Object.

Object : Top level Kotlin object

Companion Object : In class, create object under class (only one companion object into class)

To make under above, Kotlin can create Java static like

Example

Let’s create Example.

Prepare sample Project and Create

Activity : Java
Object : Kotlin
Class + Companion Object : Kotlin

Call Object and Companion Object from Java Activity

ObjectA.kt

object ObjectA {

    fun methodA() : String {
        return "MethodA"
    }
}

CompanionB.kt

class CompanionB {

    companion object CompanionInner {
        fun methodB() : String {
            return "methodB"
        }
    }
}

MainActivity.java

Let’s call above 2 from Java.

To call Object for kotlin use “INSTANCA“. This is answer

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        ObjectA.INSTANCE.methodA(); // Object
        CompanionB.CompanionInner.methodB(); // Companion Object
    }
}

Companion Object is simple, just use companion object name.