转换为Kotlin后如何访问Java接口静态变量

Question

I have a an Interface in Java with the static variable interfaceValue that I could access as below

public class Experimenting {

    public interface MyInteface {
        int interfaceValue = 10;
    }

    class MyImpl implements MyInteface { }

    MyImpl myImpl = new MyImpl();

    void testing() {
        int getInterfaceValue = myImpl.interfaceValue;
    }
}

When I convert to Kotlin, it is as below

class Experimenting {

    internal var myImpl = MyImpl()

    interface MyInteface {
        companion object {
            val interfaceValue = 10
        }
    }

    internal inner class MyImpl : MyInteface

    internal fun testing() {
        val getInterfaceValue = myImpl.interfaceValue
    }
}

However the myImpl.interfaceValue is showing compile error sign, where by it doesn't recognize the interfaceValue . How could I still access my interfaceValue in Kotlin?

Answer 1

The conversion converts the static final interfaceValue to a val in the companion Kotlins equivalent of that. Unfortunately the converter is not perfect and sometimes messes thing up. To access it

import com.your.package.Experimenting.MyInteface.Companion.interfaceValue    
class Experimenting {

    internal var myImpl = MyImpl()

    interface MyInteface {
        companion object {
           const val interfaceValue = 10
        }
    }

    internal inner class MyImpl : MyInteface

    internal fun testing() {
        val getInterfaceValue = interfaceValue
    } 
}

does the trick.

also does:

class Experimenting {

    internal var myImpl = MyImpl()

    interface MyInteface {
        companion object {
           val interfaceValue = 10
        }
    }

    internal inner class MyImpl : MyInteface

    internal fun testing() {
        val getInterfaceValue = MyInteface.interfaceValue
    }
}

A third way would be to copy the value of interfaceValue into the implementing class:

class Experimenting {

    internal var myImpl = MyImpl()

    interface MyInteface {
        companion object {
            const val interfaceValue = 10
        }
    }

    internal inner class MyImpl : MyInteface{
        val interfaceValue = MyInteface.interfaceValue
    }

    internal fun testing() {
        val getInterfaceValue = myImpl.interfaceValue
    }
}

Basically you access it like you would access a static variable in java.

Answer 2

I guess the right conversion of such Java code to Kotlin code should be as below

class Experimenting {

    internal var myImpl = MyImpl()

    interface MyInteface {

        val interfaceValue: Int
        get() = 10
    }

    internal inner class MyImpl : MyInteface

    internal fun testing() {
        val getInterfaceValue = myImpl.interfaceValue
    }
}

Though syntactically they are different, ie interfaceValue not really a static variable anymore, but practicality the same.